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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2006

Commission File No. 0-14710

XOMA Ltd.

(Exact name of registrant as specified in its charter)

Securities registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act:

Common Shares, U.S. $.0005 par value

Preference Share Purchase Rights

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ¨    No  x

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act.    Yes  ¨    No  x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    ¨

Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):    Large Accelerated Filer  ¨    Accelerated Filer  x    Non-Accelerated filer  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act of 1934).    Yes  ¨    No  x

The approximate aggregate market value of voting shares held by non-affiliates of the registrant is $164,780,665 as of June 30, 2006.

Number of Common Shares outstanding as of March 5, 2007: 129,967,472

DOCUMENTS INCORPORATED BY REFERENCE:

Portions of the Company’s Proxy Statement for the Company’s 2007 Annual General Meeting of Shareholders are incorporated by reference into Part III of this Report.

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XOMA Ltd.

2006 Form 10-K Annual Report

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PART I

Overview

XOMA Ltd. (“XOMA”), a Bermuda company, is a leading biopharmaceutical company in the field of therapeutic antibody discovery and development. XOMA’s pipeline includes both proprietary products and collaborative programs at various stages of preclinical and clinical development primarily directed toward treatments for cancer and immune disorders. XOMA possesses a broad technology platform for the discovery, optimization and manufacture of therapeutic antibodies as well as a fully integrated product development infrastructure for antibodies and other biologics. We receive royalties from Genentech, Inc. (“Genentech”) on two approved products, RAPTIVA^®, which is marketed in the United States, Europe and elsewhere, for the treatment of moderate-to-severe plaque psoriasis, and LUCENTIS^®, a new drug for the treatment of neovascular (wet) age-related macular degeneration, which is marketed in the United States and Europe. We also have future royalty interests in additional therapeutic antibody product candidates being developed by others as a result of licensing our technologies. In addition to supporting our product pipeline, we use our infrastructure to provide process development and manufacturing services on a fee-for-service basis.

Strategy

Our strategy is to develop, manufacture and gain licensure for antibodies and other recombinant protein products to treat cancer, immunological and inflammatory disorders, and infectious diseases. In addition to our own proprietary products, we broaden our pipeline by leveraging our development and manufacturing infrastructure through collaborations with other companies and research institutions. Our goal is to reduce our cash burn and drive towards profitability while continuing to strengthen our product pipeline. We recognize the challenging nature of this goal, and the principal elements of our strategy are to:

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Products

Below is a summary of our current products and stages of clinical development:

XOMA has a financial interest in two marketed antibody products and a third that has been submitted for regulatory approval, and is developing other antibody and protein therapeutic products. These products are listed below in order of their development status, beginning with the most advanced:

In 2006, Serono announced the results of the 24-week Clinical Experience Acquired with RAPTIVA^® (“CLEAR”) study to evaluate RAPTIVA^® in moderate-to-severe psoriasis patients and refractory patients. The CLEAR study confirmed the efficacy and safety of RAPTIVA^® during the initial 12-week treatment period and demonstrated a continued improvement in clinical response for patients following an extended treatment. RAPTIVA^® was also found to be equally effective in the subgroup of patients refractory to at least two systemic therapies. In 2006, Serono also initiated CLEAREST^™ in Europe with a seven year trial, the first large-scale pharmaco-epidemiological study of RAPTIVA^® in psoriasis in Europe. The primary objective of this prospective, seven year cohort study is to gather additional long-term safety data of RAPTIVA^® in 7,000 adult patients with moderate-to-severe plaque psoriasis over approximately 18,000 patient years of clinical treatment. In February of 2007, Genentech announced results from a 12-week Phase IV study of RAPTIVA^® that showed statistically significant improvement in patients with chronic moderate-to-severe plaque psoriasis involving the hands and feet. The study was the first randomized, double blind, placebo-controlled trial to evaluate a biologic agent in the treatment of this uniquely challenged subpopulation of psoriasis patients.

In January of 2007, in conjunction with Harvard Medical School, we initiated an open label, dose escalating Phase I/II clinical trial of NEUPREX^® in adults and children undergoing allogeneic hematopoietic stem cell transplantation (“HSCT”) to evaluate safety, pharmacokinetics and markers of biological activity. Earlier research indicates that endotoxemia can induce or worsen acute graft vs. host disease in these patients who are also susceptible to infectious complications due to the large doses of radiation or chemotherapy they receive prior to transplantation. We expect to add other sites to this

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study during 2007. Success in HSCT trials may be relevant to potential use in acute radiation syndrome as part of the United States Government’s bio-defense efforts.

XOMA is also supporting investigator-initiated trials at University of Texas Southwestern in Dallas in pediatric patients with congenital heart abnormalities requiring open heart surgery at Children’s Hospital and in patients with burn injuries at Parkland Burn Center. These Phase I trials are evaluating opebacan’s safety and its role in improving endotoxin-induced complications in these patient populations. We expect these trials to conclude in 2007 and then evaluate options for conducting additional studies.

In September of 2006, the European Medicines Agency (“EMEA”) granted an orphan medicinal product designation to NEUPREX^® in meningococcal sepsis, a potentially life-threatening bacterial infection predominantly affecting young children. Meningococcal sepsis is a blood infection caused by the gram-negative bacterium Neisseria meningitidis. We are completing the regulatory assessment for NEUPREX^® under the EMEA exceptional circumstances mechanism during the first half of 2007 and intend to base our planned application on existing Phase III clinical trial data.

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In October of 2004, we entered into an agreement with Triton BioSystems, Inc. (“Triton”) under which Triton has in-licensed the exclusive worldwide right to use the ING-1 monoclonal antibody with Triton’s Targeted Nano-Therapeutics^™ (“TNT^™”) System. The TNT^™ System is an innovative product that ablates tumors by using tiny magnetic spheres delivered, to the tumor, systemically with antibodies and heated by means of a magnetic field directed to the tumor. The combination of the ING-1 antibody with the TNT^™ System is intended to create a novel, highly selective, safe, and effective treatment for adenocarcinomas, such as breast, colorectal, lung, ovary and prostate. ING-1 remains available for licensing outside the field covered by the Triton license.

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The following table describes important information related to certain products on which we earn royalties, that we are currently developing or that are available for licensing:

Below is a summary of certain proprietary technologies owned by us and available for licensing to other companies:

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We have granted over 45 licenses to biotechnology and pharmaceutical companies to use our patented and proprietary technologies relating to bacterial expression of recombinant pharmaceutical products. Bacterial antibody expression is an enabling technology for the discovery and selection, as well as the development and manufacture, of recombinant protein pharmaceuticals, including diagnostic and therapeutic antibodies for commercial purposes. Bacterial antibody expression is also a key technology used in multiple systems for high-throughput screening of antibody domains. Expression of antibodies by phage display technology, for example, depends upon the expression and secretion of antibody domains from bacteria as properly folded, functional proteins.

Current licensees include but are not limited to the following companies:

These licenses are sometimes associated with broader agreements. For example, in October of 2006, we entered into a licensing and product development agreement with Affimed Therapeutics AG (“Affimed”). Under the terms of the agreement, Affimed received a license to use our BCE technology for research related to recombinant antibody products, with an option to acquire a BCE license for production and commercialization of antibodies, in particular their proprietary TandAb and Flexibody products. In addition, we will provide Affimed with cell line development and process development services specific to a TandAb therapeutic product candidate that they are currently developing. We received a license under Affimed’s antibody library patents for antibody discovery purposes, as well as for the development and commercialization of antibodies. In addition, Affimed will build two customized patient-derived human antibody phage display libraries according to our specifications.

As of February 2, 2007, we were aware of one antibody product, UCB S.A.’s (“UCB”) CIMZIA^™, in late-stage clinical testing which is manufactured under a license using our BCE technologies. CIMZIA^™ (certolizumab pegol, CDP870) is a anti-TNF (Tumor Necrosis Factor) alpha antibody fragment and has been submitted for regulatory approval for Crohn’s disease. It has had positive results in two Phase III trials in rheumatoid arthritis and in one mid-stage clinical trial in psoriasis.

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HE^™ technology was used in our XOMA 052 and certain other antibody products. In 2006, we entered into our first HE^™ technology service agreements and humanized antibodies for AVEO Pharmaceuticals, Inc. (“AVEO”) and Attenuon, LLC (“Attenuon”).

In addition, we have installed commercially available phage display libraries for the discovery of antibodies and are utilizing XOMA proprietary libraries to enhance our antibody technology platform. We believe that access to multiple libraries offers a number of benefits to XOMA and its partners, by permitting screening of libraries in parallel where feasible to increase our probability of technical and business success in finding those rare and unique, high-affinity antibodies directed to targets of interest. We also have access to certain intellectual property rights and services that augment our existing antibody technology platform and development capabilities and further streamline product development timelines. This broad antibody technology platform and expertise is available for building our antibody product pipeline as well as those of our collaborators.

Our fully integrated infrastructure also allows us to offer technical development and manufacturing services on a fee-for-service basis. In particular, in March of 2005, we were awarded an 18-month contract worth approximately $15.0 million from the National Institute of Allergy and Infectious Diseases (“NIAID”) to develop three anti-botulinum neurotoxin monoclonal antibodies and, in July of 2006, NIAID awarded an additional three year contract worth approximately $16.3 million to produce these antibodies to protect United States citizens against the harmful effects of botulinum neurotoxins used in bioterrism. In November 2006, we were named as a subcontractor under a prime contract between SRI International and NIAID. Once the final terms are negotiated, we will manufacture a variety of monoclonal antibody therapeutic agents of importance to NIAID. We expect the final contract to run five years and total $28.1 million. Successful negotiation of the subcontract would, if the full amount is funded, bring the total of our governmental contract awards to approximately $60.0 million since March of 2005. We are continuing to seek other opportunities for government and biodefense contracts.

Financial and Legal Arrangements of Product Collaborations, Licensing an Other Arrangements

Current Agreements

Genentech

In April of 1996, we entered into a collaboration agreement with Genentech for the development of RAPTIVA^®. In March of 2003, we entered into amended and expanded agreements related to all aspects of the collaboration, to reflect the then current understanding between the companies. The agreements called for us to share in the development costs and to receive a 25% share of future United States operating profits and losses and a royalty on sales outside the United States. The agreements also called for Genentech to finance our share of development costs up until first FDA marketing approval via a convertible subordinated loan, and our share of pre-launch marketing and sales costs via an additional commercial loan facility. Under the loan agreement, upon FDA approval of the product, which occurred on October 27, 2003, we elected to pay $29.6 million of the development loan in convertible preference shares and to defer repayment of the remaining $40.0 million as an offset against future proceeds from our 25% share of United States operating profits on the product. On December 22, 2003, we issued the preference shares to Genentech which are convertible into approximately 3.8 million common shares at a price of $7.75 per common share. The $13.4 million of outstanding principal and interest on the commercial loan was payable only in cash and was paid in January and May of 2004.

In January of 2005, we announced a restructuring of our arrangement with Genentech on RAPTIVA^®. Under the restructured arrangement, effective January 1, 2005, we are entitled to receive mid-single digit

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royalties on worldwide sales of RAPTIVA^® in all indications. The previous cost and profit sharing arrangement for RAPTIVA^® in the United States was discontinued, and Genentech will be responsible for all operating and development costs associated with the product. Genentech may elect and we may agree to provide further clinical trial or other development services at Genentech’s expense. In addition, our obligation to pay the outstanding balance to Genentech of $40.9 million under the development loan, including accrued interest, was extinguished.

In December of 1998, we licensed our BCE technology to Genentech, which utilized it in the development of LUCENTIS^® for the treatment of neovascular (wet) age-related macular degeneration. LUCENTIS^® was approved by the FDA in June of 2006 and in the European Union in January of 2007. We are entitled to receive an undisclosed royalty on worldwide sales of LUCENTIS^®.

Novartis

In February of 2004, we entered into an exclusive, worldwide, multi-product collaboration with Novartis to develop and commercialize antibody products for the treatment of cancer. Under the terms of the agreement, the companies agreed to jointly research, develop, and commercialize multiple antibody product candidates. The companies share expenses and revenues, generally on a 70-30 basis, with our share being 30%. Novartis’ profit share is subject to a limited upward adjustment, which, in turn, may be reduced if we achieve certain milestones. Financial terms include initial payments to us in 2004 totaling $10.0 million and a loan facility, secured by our interest in the collaboration, of up to $50.0 million to fund up to 75% of our share of expenses beginning in 2005. In the first quarter of 2007, Novartis’ and our mutual obligations to conduct antibody discovery, development and commercialization work together on an exclusive basis in oncology expired, except with respect to existing collaboration projects which have reached the development stage.

Lexicon

In June of 2005, we entered into a collaboration agreement with Lexicon to jointly develop and commercialize antibody drugs for certain targets discovered by Lexicon. The collaboration is designed to combine Lexicon’s target discovery and biotherapeutics capabilities with our antibody generation, process development and manufacturing expertise to accelerate the development and commercialization of novel therapeutic antibodies.

During the three-year initial term, Lexicon will select for submission to the collaboration targets from among those discovered and analyzed in its Genome5000^™ program. In this program, Lexicon is using its gene knockout technology to discover the physiological functions of 5,000 potential drug targets. Our role is to generate or engineer antibodies that modulate the collaboration’s targets using phage display libraries and our proprietary HE^™ technology. The companies are sharing the responsibility and costs for research, preclinical, clinical and commercialization activities. Costs and profits are allocated 65% to Lexicon and 35% to us. We will have principal responsibility for manufacturing antibodies for use in clinical trials and commercial sales.

Schering Plough

In May of 2006, we entered into a collaboration agreement with the SPRI division of Schering-Plough Corporation for therapeutic monoclonal antibody discovery and development. Under the agreement, SPRI will make upfront, annual maintenance and milestone payments to us, fund our R&D and manufacturing activities related to the agreement and pay royalties on sales of products resulting from the collaboration. During the collaboration, we will discover therapeutic antibodies against three targets selected by SPRI using multiple human antibody phage display libraries, may optimize antibodies through affinity maturation or other protein engineering, may use our proprietary HE^™ technology to humanize antibody candidates generated by hybridoma techniques, perform pre-clinical studies to support regulatory filings, develop cell lines and production processes and produce antibodies for initial clinical trials. SPRI selected the first target at the inception of the agreement and, in December of 2006, exercised its right to initiate the additional discovery and development programs.

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Takeda

In November of 2006, we entered into a collaboration agreement with Takeda for therapeutic monoclonal antibody discovery and development. During the collaboration, we will discover and optimize therapeutic antibodies against multiple targets selected by Takeda. Under the agreement, Takeda will make upfront, annual maintenance and milestone payments to us, fund our R&D and manufacturing activities for preclinical and early clinical studies and pay royalties on sales of products resulting from the collaboration. Takeda will be responsible for clinical trials and commercialization of drugs after an IND submission and is granted the right to manufacture once the product enters into Phase II clinical trials.

NIAID

In March of 2005, we were awarded a $15.0 million contract from NIAID, a division of the National Institutes of Health, to develop three anti-botulinum neurotoxin monoclonal antibody therapeutics. Under this contract, we created production cell lines using our proprietary antibody expression systems, built Master and Manufacturer’s Working Cell Banks, developed production processes and produced initial quantities of the three antibodies. The contract was performed over an eighteen month period and was 100% funded with Federal funds from NIAID under Contract No. HHSN266200500004C. Final acceptance of the project was received in October of 2006.

In July of 2006, we were awarded a $16.3 million contract funded with Federal funds from NIAID under Contract No. HHSN266200600008C/N01-Al-60008 to produce monoclonal antibodies for the treatment of botulism to protect United States citizens against the harmful effects of botulinum neurotoxins used in bioterrorism. Under this contract, we will create and produce an innovative injectable product comprised of three anti-type A botulinum neurotoxin monoclonal antibodies to support entry into Phase I safety human clinical trials. The work is being performed on a cost plus fixed fee basis, per the terms of the contract, over a three year period.

Taligen

In September of 2006, we entered into an agreement with Taligen Therapeutics, Inc. (“Taligen”) which formalized an earlier letter agreement, which was signed in May of 2006, for the development and Good Manufacturing Practices (“cGMP”) manufacture of a novel antibody fragment for the potential treatment of inflammatory diseases. Under the agreement, we will utilize our BCE technology and expertise to develop and scale-up production processes for Taligen’s FAb antibody fragment and manufacture quantities of the antibody fragment sufficient to support preclinical and initial clinical trials. Taligen will pay all manufacturing costs and, if it elects to exercise its option to obtain a production license for our BCE technology, will make upfront, milestone and royalty payments.

AVEO

In April of 2006, we entered into an agreement with AVEO to utilize our HE^™ technology to humanize AV-299 under which AVEO paid us an up-front license fee and development milestones. Under this agreement we created four HE^™ versions of the original AV-299, all of which met design goals and from which AVEO selected one as its lead development candidate. In the future, AVEO will pay annual maintenance fees, additional development milestones and royalties.

In September of 2006, as a result of the successful humanization of AV-299, we entered into a second agreement with AVEO to manufacture and supply AV-299, AVEO’s novel anti-HGF antibody, in support of early clinical trials. Under the agreement, we will create AV-299 production cell lines and conduct process and assay development as well as cGMP manufacturing activities in support of AVEO’s IND filing and early clinical trials. AVEO retains all development and commercialization rights to AV-299.

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Attenuon

In September of 2006, we entered into an agreement with Attenuon to utilize our HE^™ technology to humanize a monoclonal antibody targeting the urokinase plasminogen activator system for the treatment of cancer. Attenuon will pay us an up-front fee, annual maintenance fees, development milestones and royalties. Attenuon will retain all development and commercialization rights to the antibody.

Triton

In October of 2004, we entered into an agreement with Triton under which Triton licensed the exclusive worldwide rights from us to use our ING-1 monoclonal antibody with Triton’s TNT^™ System. The TNT^™ System is an innovative product that ablates tumors by using tiny magnetic spheres delivered, to the tumor, systemically with antibodies and heated by means of a magnetic field directed to the tumor. The combination of the ING-1 antibody with the TNT^™ System is intended to create a novel, highly selective, safe, and effective treatment for adenocarcinomas, such as breast, colorectal, lung, ovary and prostate. The license to Triton includes United States and foreign patent rights related to our ING-1 and HE^™ technologies along with several pending applications. ING-1 remains available for licensing outside the field covered by the Triton license. Under the terms of the contract, we received an upfront license fee and will receive milestones and royalties.

Millennium

In November of 2001, in conjunction with Millennium, we announced an agreement under which we would collaborate to develop two of Millennium’s biotherapeutic agents, MLN2222 (also known as CAB2) and MLN2201, for certain vascular inflammation indications.

In October of 2003, we announced the discontinuation of development of MLN2201, based on preliminary data from a Phase I study that did not meet predefined criteria necessary to support further product development efforts.

In December of 2003, we announced the initiation of a Phase I clinical program for MLN2222, a complement inhibitor for coronary artery bypass graft surgery targeting vascular inflammation associated with such surgery, to evaluate its safety, tolerability, pharmacokinetic and pharmacodynamic properties. In October of 2004, we announced the amendment of our agreements with Millennium whereby Millennium assumed responsibility for all development work and expenses for MLN2222 upon initiation of Phase II testing. We completed a Phase I trial of MLN2222 and have transferred the relevant clinical data from the trial to Millennium. We are obligated to continue to provide quantities of bulk drug substance and services requested and paid for by Millennium for future clinical trials. We will be entitled to receive an undisclosed royalty on future net sales of MLN2222, as well as payments related to the achievement of certain clinical and regulatory milestones.

Recently Terminated Agreements

Cubist

In September of 2005, we announced that we had signed a letter agreement with Cubist Pharmaceuticals, Inc. (“Cubist”) to develop production processes and to manufacture HepeX-B^™, a novel two-antibody biologic, in quantities sufficient to conduct Phase III clinical trials. HepeX-B^™ is a combination of two fully human monoclonal antibodies that target hepatitis B virus (“HBV”) surface antigens. In July of 2006, Cubist announced that it had decided to cease investment in this product because of stringent FDA requirements for regulatory approval and, as a result, we have terminated our letter agreement with Cubist.

Aphton

In September of 2004, we announced a worldwide collaboration with Aphton Corporation (“Aphton”) to develop treatments for gastrointestinal and other gastrin-sensitive cancers using anti-gastrin monoclonal

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antibodies. Under the terms of the agreement, the companies agreed to share all development expenses and all commercialization profits and losses for all product candidates on a 70/30 basis, with our share being 30%. In January of 2006, Aphton announced that its common stock had been delisted from Nasdaq. In May of 2006, Aphton filed for bankruptcy protection under Chapter 11, Title 11 of the United States bankruptcy code and we terminated the agreement. In July of 2006, Receptor BioLogix, Inc. acquired the assets of Aphton.

Other Products

We are seeking development and marketing partners for additional products in our pipeline. No assurance can be given regarding the timing or likelihood of future collaborative arrangements or of product licensure.

We are also pursuing additional opportunities to further broaden our product pipeline. These include product development collaborations with other pharmaceutical and biotechnology companies and evaluations of product in-licensing and acquisition opportunities.

Competition

The biotechnology and pharmaceutical industries are subject to continuous and substantial technological change. Competition in the areas of recombinant DNA-based and antibody-based technologies is intense and expected to increase as new technologies emerge and established biotechnology firms and large chemical and pharmaceutical companies continue to advance in the field. A number of these large pharmaceutical and chemical companies have enhanced their capabilities by entering into arrangements with or acquiring biotechnology companies or entering into business combinations with other large pharmaceutical companies. Many of these companies have significantly greater financial resources, larger research and development and marketing staffs and larger production facilities than ours. Moreover, certain of these companies have extensive experience in undertaking preclinical testing and human clinical trials. These factors may enable other companies to develop products and processes competitive with or superior to ours. In addition, a significant amount of research in biotechnology is being carried out in universities and other non-profit research organizations. These entities are becoming increasingly interested in the commercial value of their work and may become more aggressive in seeking patent protection and licensing arrangements. There can be no assurance that developments by others will not render our products or technologies obsolete or uncompetitive.

Without limiting the foregoing, we are aware that:

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In addition to LUCENTIS^®, there are two other FDA-approved therapies to treat macular degeneration: Pfizer, Inc.’s and OSI Pharmaceuticals, Inc.’s Macugen^® and Novartis’ and QLT Inc.’s Visudyne^®. It is also possible that LUCENTIS^® will compete with Genentech’s cancer drug Avastin^®.

There are several companies developing topical peptide treatments which may compete with XOMA 629 in acne. Migenix Inc. and its partner Cutanea Life Sciences, Inc. are developing CLS001 (formerly MBI 594AN) for roseasea, a topical peptide that has completed two Phase II trials for the treatment of acne. Helix Biomedix, Inc. is developing several peptide compounds. Medicis Pharmaceutical Corp. has rights to human derived antimicrobial peptides that may be developed for acne.

In collaboration with Novartis, we are co-developing a humanized antibody to the target CD40, and, at the current time, there are several CD40-related programs under development, mostly focused on the development of CD40 ligand products. For example, SGN-40 is a humanized monoclonal antibody under development by Seattle Genetics, Inc. (“Seattle Genetics”) which is targeting CD40 antigen. Seattle Genetics is currently conducting a phase II clinical trial for patients with diffuse large B-cell lymphoma, the most common type of aggressive non-Hodgkin’s lymphoma, and phase I trials for patients with multiple myeloma or chronic lymphocytic leukemia. In January of 2007, Seattle Genetics entered into an exclusive worldwide license agreement with Genentech to develop and commercialize SGN-40. Under the agreement, Genentech will fund future research, development, manufacturing and commercialization costs. In January of 2007, Kirin Brewery Company, Limited and Astellas Pharma Inc. announced that they have entered into a license and collaborative research and development agreement under which they will exclusively collaborate in developing and marketing a fully human anti-CD40 antagonistic monoclonal antibody worldwide with a first target indication of prophylaxis of organ rejection associated with organ transplantation.

It is possible that other companies may be developing other products based on the same human protein as our NEUPREX^® product, and these products may prove to be more effective than NEUPREX^®. It is also possible that other companies may be developing other products based on the same therapeutic target as our XOMA 052 product and these products may prove to be more effective than XOMA 052.

Regulatory

Our products are subject to comprehensive preclinical and clinical testing requirements and to approval processes by the FDA and by similar authorities in other countries. Our products are primarily regulated on a

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product-by-product basis under the United States Food, Drug and Cosmetic Act and Section 351(a) of the Public Health Service Act. Most of our human therapeutic products are or will be classified as biologic products. Approval of a biologic for commercialization requires licensure of the product and the manufacturing facilities. The review of therapeutic biologic products is carried out by the FDA’s Center for Drug Evaluation and Research, the body that also reviews drug products.

The FDA regulatory process is carried out in several phases. Prior to beginning human clinical testing of a proposed new biologic product, an IND is filed with the FDA. This document contains scientific information on the proposed product, including results of testing of the product in animal and laboratory models. Also included is information on manufacture of the product and studies on toxicity in animals and a clinical protocol outlining the initial investigation in humans.

The initial stage of clinical testing, Phase I, ordinarily encompasses safety, pharmacokinetic and pharmacodynamic evaluations. Phase II testing encompasses investigation in specific disease states designed to provide preliminary efficacy data and additional information on safety. Phase III studies are designed to further establish clinical safety and efficacy and to provide information allowing proper labeling of the product following approval. Phase III studies are most commonly multi-center, randomized, placebo-controlled trials in which rigorous statistical methodology is applied to clinical results. Other designs may also be appropriate in specific circumstances.

Following completion of clinical trials, a Biologics License Application is submitted to the FDA to request marketing approval. Internal FDA committees are formed that evaluate the application, including scientific background information, animal and laboratory efficacy studies, toxicology, manufacturing facility and clinical data. During the review process, a dialogue between the FDA and the applicant is established in which FDA questions are raised and additional information is submitted. During the final stages of the approval process, the FDA generally requests presentation of clinical or other data before an FDA advisory committee, at which point, some or all of such data may become available. Also, during the later stages of review, the FDA conducts an inspection of the manufacturing facility to establish that the product is made in conformity with good manufacturing practice. If all outstanding issues are satisfactorily resolved and labeling established, the FDA issues a license for the product and for the manufacturing facility, thereby authorizing commercial distribution.

The FDA has substantial discretion in both the product approval process and the manufacturing approval process. It is not possible to predict at what point, or whether, the FDA will be satisfied with our submissions or whether the FDA will raise questions which may delay or preclude product approval or manufacturing facility approval. As additional clinical data is accumulated, it will be submitted to the FDA and may have a material impact on the FDA product approval process. Given that regulatory review is an interactive and continuous process, we have adopted a policy of limiting announcements and comments upon the specific details of the ongoing regulatory review of our products, subject to our obligations under the securities laws, until definitive action is taken. There can be no assurance any of the products we have under development will be developed successfully, obtain the requisite regulatory approval or be successfully manufactured or marketed.

In Europe, most of our human therapeutic products are or will be classified as biological medicinal products which are assessed through a centralized procedure by the EMEA. The EMEA coordinates the evaluation and supervision of medicinal products throughout the European Union and the European Economic Area. The assessment of the Marketing Authorization (“MA”) Application is carried out by a Rapporteur and a Co-rapporteur appointed by the Committee for Medicinal Products for Human Use (“CHMP”), which is the expert scientific committee of the EMEA.

The Rapporteur and Co-rapporteur are drawn from the CHMP membership representing member states of the European Union. In addition to their responsibility for undertaking scientific assessments of an application for a MA, the Rapporteur and the Co-Rapporteur liaise with the applicant on behalf of the CHMP in an effort to provide answers to queries raised by the CHMP. Their assessment report(s) is circulated to and considered by the

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full CHMP membership, leading to the production ultimately of a CHMP opinion which is transmitted to the applicant and the European Commission. The final decision on the grant of a MA is made by the Commission as the licensing authority of the European Community (“Community”). Under Community law, a positive decision issued by the European Commission represents the grant of a MA. Such an authorization allows a medicinal product to be placed on the European market. Upon the grant of an MA in the European Union, certain member states require pricing approval before the product can be placed into commercial distribution.

Under Community law, the applicant may request grant of a MA under exceptional circumstances if comprehensive data on the efficacy and safety of the drug, under normal conditions of use cannot be provided because its intended indications are encountered so rarely (such as in the case of a medicinal product intended for treating an orphan disease) that comprehensive evidence cannot reasonably be collected, the present state of scientific knowledge will not allow comprehensive information to be collected, or it would be against generally accepted medical ethics to collect comprehensive information. The Rapporteur, Co-Rapporteur and the other CHMP members will assess the justification/data submitted for exceptional circumstances as part of the overall assessment of the benefit/risk of the application. It is up to the CHMP, during the review, to ultimately decide on whether grant of a MA under exceptional circumstances is justified on the evidence before them. Approval under exceptional circumstances is subject to a requirement for specific procedures related to safety and results of its use and is reviewed annually to reassess the risk-benefit balance of the product. Once approval is granted, the product can be marketed under the single European MA in all member states of the European Union and the European Economic Area. Consistent with the single MA, the labeling for Europe is identical throughout all member states except that all labeling must be translated into the local language of the country of intended importation and in relation to the content of the so called “blue box” on the outer packaging in which locally required information may be inserted.

Orphan drugs are those intended for use in rare diseases or conditions. As a result of the high cost of development and the low return on investment for rare diseases, governments provide regulatory and commercial incentives for the development of drugs for small disease populations. In the United States, the term “rare disease or condition” means any disease or condition which affects less than 200,000 persons in the United States. Applications for United States orphan drug status are evaluated and granted by the Office of Orphan Products Development (“OOPD”) of the FDA. In the United States, orphan drugs are subject to the standard regulatory process for marketing approval but are exempt from the payment of user fees for licensure, receive market exclusivity for a period of seven years and some tax benefits, and are eligible for OOPD grants. In Europe, orphan medicinal products are those intended for the diagnosis, prevention or treatment of a life-threatening or chronically debilitating condition affecting not more than five in 10,000 persons in the Community. The EMEA’s Committee for Orphan Medicinal Products (“COMP”) reviews applications seeking orphan designation. If the European Commission agrees with a positive assessment made by COMP, then the product will receive a positive designation through adoption of a decision by the European Commission. Orphan medicinal products are exempt from fees for protocol assistance and scientific advice from the Scientific Advice Working Party during development, reduction or exemption of MA and other fees, and ten year market exclusivity upon granting of a MA in respect of the approved clinical indication. Moreover, manufacturers may be eligible for grants or other financial incentives from the Community and Member States programs.

Patents and Trade Secrets

As a result of our ongoing activities, we hold and are in the process of applying for a number of patents in the United States and internationally to protect our products and important processes. We also have obtained or have the right to obtain exclusive licenses to certain patents and applications filed by others. However, the patent position of biotechnology companies generally is highly uncertain and no consistent policy regarding the breadth of allowed claims has emerged from the actions of the U.S. Patent and Trademark Office (“Patent Office”) with respect to biotechnology patents. Accordingly, no assurance can be given that our patents will afford protection against competitors with similar technologies, or others will not obtain patents claiming aspects similar to those covered by our patent applications.

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We have established an extensive portfolio of patents and applications related to our BPI-related products, including novel compositions, their manufacture, formulation, assay and use. We are also the exclusive licensee of BPI-related patents and applications owned by New York University (“NYU”), including those directed to novel BPI-related protein and DNA compositions, as well as their production and uses. Finally, we are the exclusive licensee of BPI-related patents and applications owned by Incyte Corporation (“Incyte”), including those related to endotoxin-associated uses of BPI.

We have established a portfolio of patents related to our bacterial expression technology, including claims to novel promoter sequences, secretion signal sequences, compositions, methods for expression and secretion of recombinant proteins from bacteria, including immunoglobulin gene products, and improved methods and cells for expression of recombinant protein products. U.S. Patent No. 5,028,530 is directed to expression vehicles containing an araB promoter, host cells and processes for regulated expression of recombinant proteins. U.S. Patent Nos. 5,576,195 and 5,846,818 are related to DNA encoding a pectate lyase signal sequence, recombinant vectors, host cells and methods for production and externalization of recombinant proteins. U.S. Patent Nos. 5,595,898, 5,698,435 and 5,618,920 address secretable immunoglobulin chains, DNA encoding the chains and methods for their recombinant production. U.S. Patent Nos. 5,693,493, 5,698,417 and 6,204,023 relate to methods for recombinant production/secretion of functional immunoglobulin molecules. U.S. Patent No. 7,094,579 relates to eukaryotic signal sequences and their use in methods for prokaryotic expression of recombinant proteins. U.S. Patent No. 6,803,210 relates to improved bacterial host cells that are deficient in one or more of the active transport systems for an inducer of an inducible promoter, such as arabinose for an araB promoter, and methods for the use of such cells for the production of recombinant proteins.

We have also established a portfolio of patent applications related to our mammalian expression technology, including U.S. Patent Application Publication No. 2003/0203447 for which we have received a Notice of Allowance, related to methods and materials for increasing the expression of recombinant polypeptides using expression vectors containing multiple copies of a transcription unit encoding a polypeptide of interest.

We have established a portfolio of patents and applications related to our HE^™ technology, including U.S. Patent No. 5,766,886, directed to methods of modifying antibody variable domains to reduce immunogenicity. Related patents and applications are directed to antibodies engineered according to our patented methods. We believe that our patented HE^™ technology provides an attractive alternative to other humanization technologies.

If certain patents issued to others are upheld or if certain patent applications filed by others issue and are upheld, we may require certain licenses from others in order to develop and commercialize certain potential products incorporating our technology. There can be no assurance that such licenses, if required, will be available on acceptable terms.

Research and License Agreements

We have contracted with a number of academic and institutional collaborators to conduct research and development activities. Under these agreements, we generally fund either the research and development or evaluation of products, technologies or both, will own or obtain exclusive licenses to products or technologies developed and may pay royalties on sales of products covered by certain licenses. The rates and durations of such royalty payments vary by product and institution and range, generally, for periods from five years to indefinite duration. Aggregate expenses incurred by us under all of our research agreements were negligible for each of 2006, 2005 and 2004. We have entered into certain license agreements with respect to the following products:

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Each party has the right to terminate the agreement upon a material breach by the other party of the performance of its obligations under the agreement, subject to customary cure periods. Upon termination of the agreement prior to the expiration of the relevant patents, all rights in and to NYU’s intellectual property revert to NYU.

The agreement expires in July of 2008 unless, on or prior to such date, the license granted therein becomes fully paid up in accordance with its terms. Incyte has the right to terminate the agreement (subject to a customary cure period) upon a breach by us of any of our material obligations under the agreement.

International Operations

We believe that, because the pharmaceutical industry is global in nature, international activities will be a significant part of our future business activities and that, when and if we are able to generate income, a substantial portion of that income will be derived from product sales and other activities outside the United States.

A number of risks are inherent in international operations. Foreign regulatory agencies often establish standards different from those in the United States. An inability to obtain foreign regulatory approvals on a timely basis could have an adverse effect on our international business, financial condition and results of operations. International operations may be limited or disrupted by the imposition of government controls, export license requirements, political or economic instability, trade restrictions, changes in tariffs, restrictions on repatriating profits, taxation or difficulties in staffing and managing international operations. In addition, our business, financial condition and results of operations may be adversely affected by fluctuations in currency exchange rates. There can be no assurance that we will be able to successfully operate in any foreign market.

We were incorporated in Delaware in 1981 and became a Bermuda company effective December 31, 1998, when we completed a shareholder-approved corporate reorganization, changing our legal domicile from Delaware to Bermuda and our name to XOMA Ltd. When referring to a time or period before December 31, 1998, or when the context so requires, the terms “Company” and “XOMA” refer to XOMA Corporation, a Delaware corporation and the predecessor of XOMA Ltd.

Employees

As of December 31, 2006, we employed 255 non-unionized full-time employees at our California facilities, principally in Berkeley, California, and one employee in Ireland. Our employees are engaged in clinical, process development and manufacturing, quality assurance and control, research and product development, and in executive, finance and administrative positions. We consider our employee relations to be excellent.

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Available Information

For information on XOMA’s investment prospects and risks, please contact Mr. Paul Goodson, Senior Director, Investor Relations and Corporate Communications at (800) 246-9662 or by sending an e-mail message to investorrelations@xoma.com. Our principal executive offices are located at 2910 Seventh Street, Berkeley, California 94710 U.S.A. Our telephone number is (510) 204-7200.

The following information can be found on our website at http://www.xoma.com or can be obtained free of charge by contacting our Investor Relations Department:

We intend to satisfy the applicable disclosure requirements regarding amendments to, or waivers from, provisions of our Code of Ethics by posting such information on our website.

The following risk factors and other information included in this annual report should be carefully considered. The risks and uncertainties described below are not the only ones we face. Additional risks and uncertainties not presently known to us also may impair our business operations. If any of the following risks occur, our business, financial condition, operating results and cash flows could be materially adversely affected.

Our present and future revenues rely significantly on sales of products marketed and sold by others.

Currently, our revenues rely significantly upon sales of RAPTIVA^® and LUCENTIS^®, in which we have only royalty interests. RAPTIVA^® was approved by the FDA on October 27, 2003, for the treatment of chronic moderate-to-severe plaque psoriasis in adults who are candidates for systemic therapy or phototherapy. Genentech and Serono, Genentech’s international marketing partner for RAPTIVA^®, are responsible for the marketing and sales effort in support of this product. In September of 2004, Serono announced that RAPTIVA^® had received approval for use in the European Union and the product was launched in several European Union countries in the fourth quarter of 2004. In January of 2007, Merck KGaA acquired Serono and renamed the surviving entity Merck Serono S.A. We are evaluating the impact of this acquisition but do not yet know what effect it will have on sales of RAPTIVA^®. LUCENTIS^® was approved by the FDA on June 30, 2006, for the treatment of age-related macular degeneration. Genentech and Novartis, Genentech’s international marketing partner for LUCENTIS^®, are responsible for the marketing and sales effort in support of this product. We have no role in marketing and sales efforts, and Genentech, Serono and Novartis do not have an express contractual obligation to us regarding the marketing or sales of RAPTIVA^® or LUCENTIS^®.

Under our current arrangements with Genentech, we are entitled to receive royalties on worldwide sales of RAPTIVA^® and LUCENTIS^®. Successful commercialization of these products is subject to a number of risks, including, but not limited to:

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According to Genentech, United States sales of RAPTIVA^® during 2006 were $89.8 million, compared with $79.2 million and $52.4 million during 2005 and 2004, respectively. According to Serono, sales of RAPTIVA^® outside of the United States during 2006 were $69.9 million, compared with $33.4 million and $3.9 million during 2005 and 2004, respectively. According to Genentech, United States sales of LUCENTIS^® were $380.0 million and sales outside the United States were $27.0 million during 2006. LUCENTIS^® sales began on June 30, 2006, upon its approval by regulatory agencies. Given our current reliance on RAPTIVA^® and LUCENTIS^® as principal sources of our revenues, any material adverse developments with respect to the commercialization of RAPTIVA^® or LUCENTIS^® may cause our revenues to decrease and may cause us to incur losses in the future.

Because our products are still being developed, we will require substantial funds to continue; we cannot be certain that funds will be available and, if they are not available, we may have to take actions which could adversely affect your investment.

If adequate funds are not available, we may have to raise additional funds in a manner that may dilute or otherwise adversely affect the rights of existing shareholders, curtail or cease operations, or file for bankruptcy protection in extreme circumstances. We have spent, and we expect to continue to spend, substantial funds in connection with:

Based on current spending levels, anticipated revenues, collaborator funding, proceeds from our convertible note offerings in February of 2005 and February of 2006, our November 2006 term loan and other sources of funding we believe to be available, we estimate that we have sufficient cash resources to meet our anticipated net cash needs through at least 2008. Any significant revenue shortfalls, increases in planned spending on development programs or more rapid progress of development programs than anticipated, as well as the unavailability of anticipated sources of funding, could shorten this period. Progress or setbacks by potentially competing products may also affect our ability to raise new funding on acceptable terms. As a result, we do not know when or whether:

Cash balances and operating cash flow are influenced primarily by the timing and level of payments by our licensees and development partners, as well as by our operating costs.

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Our level of leverage and debt service obligations could adversely affect our financial condition.

As of December 31, 2006, we (including our subsidiaries) had approximately $98.2 million, including our embedded derivative, of indebtedness outstanding. We may not be able to generate cash sufficient to pay the principal of, interest on and other amounts due in respect of our indebtedness when due. We and our subsidiaries may also incur additional debt that may be secured. In connection with our collaboration with Novartis, Novartis has extended a line of credit to us (through our U.S subsidiary) for $50.0 million to fund up to 75% of our expenses thereunder, of which $16.4 million was drawn as of December 31, 2006. This line of credit is secured by a pledge of our interest in the collaboration. On November 9, 2006, XOMA (US) LLC entered into a five-year, $35.0 million term loan facility with Goldman Sachs Specialty Lending Holdings, Inc. (“Goldman Sachs”) and borrowed the full amount thereunder. The loan is guaranteed by XOMA and is secured by the payment rights due to XOMA (US) LLC relating to RAPTIVA^®, LUCENTIS^® and CIMZIA^™. As a result, these assets will not be available to XOMA or any other lender to secure future indebtedness.

Our level of debt and debt service obligations could have important effects on us and our investors. These effects may include:

Our ability to satisfy our debt obligations will depend upon our future operating performance and the availability of refinancing debt. If we are unable to service our debt and fund our business, we may be forced to reduce or delay capital expenditures, seek additional debt financing or equity capital, restructure or refinance our debt or sell assets. We cannot assure you that we would be able to obtain additional financing, refinance existing debt or sell assets on satisfactory terms or at all.

Most of our therapeutic products have not received regulatory approval. If these products do not receive regulatory approval, neither our third party collaborators nor we will be able to manufacture and market them.

Our products cannot be manufactured and marketed in the United States and other countries without required regulatory approvals. The United States government and governments of other countries extensively regulate many aspects of our products, including:

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In the United States, the FDA regulates pharmaceutical products under the Federal Food, Drug, and Cosmetic Act and other laws, including, in the case of biologics, the Public Health Service Act. At the present time, we believe that most of our products will be regulated by the FDA as biologics. Changes in the regulatory approval policy during the development period, changes in, or the enactment of, additional regulations or statutes or changes in regulatory review for each submitted product application may cause delays in the approval or rejection of an application. Even if the FDA or other regulatory agency approves a product candidate, the approval may impose significant restrictions on the indicated uses, conditions for use, labeling, advertising, promotion, marketing and/or production of such product. Even for approved products such as RAPTIVA^® and LUCENTIS^®, the FDA may impose ongoing requirements for post-approval studies, including additional research and development and clinical trials, and may subsequently withdraw approval based on these additional trials. The FDA and other agencies also may impose various civil or criminal sanctions for failure to comply with regulatory requirements, including withdrawal of product approval. State regulations may also affect our proposed products. The FDA has substantial discretion in both the product approval process and manufacturing facility approval process and, as a result of this discretion and uncertainties about outcomes of testing, we cannot predict at what point, or whether, the FDA will be satisfied with our or our collaborators’ submissions or whether the FDA will raise questions which may be material and delay or preclude product approval or manufacturing facility approval. As we accumulate additional clinical data, we will submit it to the FDA, which may have a material impact on the FDA product approval process.

We face uncertain results of clinical trials of our potential products.

Our potential products will require significant additional research and development, extensive preclinical studies and clinical trials and regulatory approval prior to any commercial sales. This process is lengthy and expensive, often taking a number of years. As clinical results are frequently susceptible to varying interpretations that may delay, limit or prevent regulatory approvals, the length of time necessary to complete clinical trials and to submit an application for marketing approval for a final decision by a regulatory authority varies significantly. As a result, it is uncertain whether:

For example,

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Given that regulatory review is an interactive and continuous process, we maintain a policy of limiting announcements and comments upon the specific details of regulatory review of our products, subject to our obligations under the securities laws, until definitive action is taken.

Because all of our products are still being developed, we have sustained losses in the past and we expect to sustain losses in the future.

We have experienced significant losses and, as of December 31, 2006, we had an accumulated deficit of $727.5 million.

For the year ended December 31, 2006, we had a net loss of approximately $51.8 million or $0.54 per common share (basic and diluted). For the year ended December 31, 2005, as a result of the restructuring of our Genentech arrangement and subsequent extinguishment of our obligation to pay $40.9 million under a development loan and related one-time credit to other income, we had net income of approximately $2.8 million or $0.03 per common share (basic and diluted).

Our ability to achieve profitability is dependent in large part on the success of our development programs, obtaining regulatory approval for our products and entering into new agreements for product development, manufacturing and commercialization, all of which are uncertain. Our ability to fund our ongoing operations is dependent on the foregoing factors and on our ability to secure additional funds. Because our products are still being developed, we do not know whether we will ever achieve sustained profitability or whether cash flow from future operations will be sufficient to meet our needs.

Our agreements with third parties, many of which are significant to our business, expose us to numerous risks.

Our financial resources and our marketing experience and expertise are limited. Consequently, our ability to successfully develop products depends, to a large extent, upon securing the financial resources and/or marketing capabilities of third parties.

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Because our collaborators and licensees are independent third parties, they may be subject to different risks than we are and have significant discretion in determining the efforts and resources they will apply. If these collaborators and licensees do not successfully develop and market these products, we may not have the capabilities, resources or rights to do so on our own. We do not know whether our collaborators or licensees will successfully develop and market any of the products that are or may become the subject of one of our collaboration or licensing arrangements. In particular, each of these arrangements provides for either sharing of collaboration expenses, which means that not only we but our collaborators must have sufficient available funds for the collaborations to continue, or funding solely by our collaborators or licensees. In addition, our collaboration with Novartis provides for funding by it in the form of a line of credit to us, and we cannot be certain that Novartis will provide the necessary funds available when we attempt to draw on the line of credit. Furthermore, our contracts with NIAID contain numerous standard terms and conditions provided for in the applicable federal acquisition regulations and customary in many government contracts. Uncertainty exists as to whether we will be able to comply with these terms and conditions in a timely manner, if at all. In addition, given our relative lack of experience in programs under contract with government agencies, we are uncertain as to the extent of NIAID’s demands and the flexibility that will be granted to us in meeting those demands. Lastly, CIMZIA^™ (CDP870) has not received marketing approval from the FDA or any foreign governmental agency, and therefore we cannot assure you that it will prove to be safe and effective, will be approved for marketing or will be successfully commercialized.

Even when we have a collaborative relationship, other circumstances may prevent it from resulting in successful development of marketable products.

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Although we continue to evaluate additional strategic alliances and potential partnerships, we do not know whether or when any such alliances or partnerships will be entered into.

Certain of our technologies are relatively new and are in-licensed from third parties, so our capabilities using them are unproven and subject to additional risks.

We license technologies from third parties. These technologies include but are not limited to phage display technologies licensed to us in connection with our BCE technology licensing program. However, our experience with some of these technologies remains relatively limited and, to varying degrees, we are still dependent on the licensing parties for training and technical support for these technologies. In addition, our use of these technologies is limited by certain contractual provisions in the licenses relating to them and, although we have obtained numerous licenses, intellectual property rights in the area of phage display are particularly complex. If the owners of the patent rights underlying the technologies we license do not properly maintain or enforce those patents, our competitive position and business prospects could be harmed. Our success will depend in part on the ability of our licensors to obtain, maintain and enforce our licensed intellectual property. Our licensors may not successfully prosecute the patent applications to which we have licenses, or our licensors may fail to maintain existing patents. They may determine not to pursue litigation against other companies that are infringing these patents, or they may pursue such litigation less aggressively than we would. Our licensors may also seek to terminate our license, which could cause us to lose the right to use the licensed intellectual property and adversely affect our ability to commercialize our technologies, products or services.

Our share price may be volatile and there may not be an active trading market for our common shares.

There can be no assurance that the market price of our common shares will not decline below its present market price or that there will be an active trading market for our common shares. The market prices of biotechnology companies have been and are likely to continue to be highly volatile. Fluctuations in our operating results and general market conditions for biotechnology stocks could have a significant impact on the volatility of our common share price. We have experienced significant volatility in the price of our common shares. From January 1, 2006 through March 5, 2007, our share price has ranged from a high of $3.50 to a low of $1.57. On March 5, 2007, the closing price of the common shares as reported on the Nasdaq National Market was $2.84 per share. Factors contributing to such volatility include, but are not limited to:

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We or our third party collaborators or licensees may not have adequate manufacturing capacity sufficient to meet market demand.

Genentech is responsible for manufacturing or arranging for the manufacturing of commercial quantities of RAPTIVA^® and LUCENTIS^®. Should Genentech have difficulty in providing manufacturing capacity to produce these products in sufficient quantities, we do not know whether they will be able to meet market demand. If not, we will not realize revenues from the sales of these products. If any of our other products are approved, because we have never commercially introduced any pharmaceutical products, we do not know whether the capacity of our existing manufacturing facilities can be increased to produce sufficient quantities of our products to meet market demand. Also, if we or our third party collaborators or licensees need additional manufacturing facilities to meet market demand, we cannot predict that we will successfully obtain those facilities because we do not know whether they will be available on acceptable terms. In addition, any manufacturing facilities acquired or used to meet market demand must meet the FDA’s quality assurance guidelines.

We do not know whether there will be, or will continue to be, a viable market for the products in which we have an ownership or royalty interest.

Although RAPTIVA^® was approved in the United States in October of 2003 and in the European Union in 2004 and LUCENTIS^® was approved in June of 2006 and in the European Union in January of 2007, their acceptance in the marketplace may not continue. Furthermore, even if other products in which we have an interest receive approval in the future, they may not be accepted in the marketplace. In addition, we or our collaborators or licensees may experience difficulties in launching new products, many of which are novel and based on technologies that are unfamiliar to the healthcare community. We have no assurance that healthcare providers and patients will accept such products, if developed. For example, physicians and/or patients may not accept a product for a particular indication because it has been biologically derived (and not discovered and developed by more traditional means) or if no biologically derived products are currently in widespread use in that indication. Similarly, physicians may not accept a product, such as RAPTIVA^® or LUCENTIS^®, if they believe other products to be more effective or are more comfortable prescribing other products. Safety concerns may also arise in the course of on-going clinical trials or patient treatment as a result of adverse events or reactions.

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Furthermore, government agencies, as well as private organizations involved in healthcare, from time to time publish guidelines or recommendations to healthcare providers and patients. Such guidelines or recommendations can be very influential and may adversely affect the usage of any products we may develop directly (for example, by recommending a decreased dosage of a product in conjunction with a concomitant therapy or a government entity withdrawing its recommendation to screen blood donations for certain viruses) or indirectly (for example, by recommending a competitive product over our product). Consequently, we do not know if physicians or patients will adopt or use our products for their approved indications.

Products and technologies of other companies may render some or all of our products noncompetitive or obsolete.

Developments by others may render our products or technologies obsolete or uncompetitive. Technologies developed and utilized by the biotechnology and pharmaceutical industries are continuously and substantially changing. Competition in the areas of genetically engineered DNA-based and antibody-based technologies is intense and expected to increase in the future as a number of established biotechnology firms and large chemical and pharmaceutical companies advance in these fields. Many of these competitors may be able to develop products and processes competitive with or superior to our own for many reasons, including that they may have:

These factors may enable others to develop products and processes competitive with or superior to our own or those of our collaborators. In addition, a significant amount of research in biotechnology is being carried out in universities and other non-profit research organizations. These entities are becoming increasingly interested in the commercial value of their work and may become more aggressive in seeking patent protection and licensing arrangements. Furthermore, positive or negative developments in connection with a potentially competing product may have an adverse impact on our ability to raise additional funding on acceptable terms. For example, if another product is perceived to have a competitive advantage, or another product’s failure is perceived to increase the likelihood that our product will fail, then investors may choose not to invest in us on terms we would accept or at all.

Without limiting the foregoing, we are aware that:

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In addition to LUCENTIS^®, there are two other FDA-approved therapies to treat macular degeneration: Pfizer, Inc.’s and OSI Pharmaceuticals, Inc.’s Macugen^® and Novartis’ and QLT Inc.’s Visudyne^®. It is also possible that LUCENTIS^® will compete with Genentech’s cancer drug Avastin^®.

There are several companies developing topical peptide treatments which may compete with XOMA 629 in acne. Migenix Inc. and its partner Cutanea Life Sciences, Inc. are developing CLS001 (formerly MBI 594AN) for roseasea, a topical peptide that has completed two Phase II trials for the treatment of acne. Helix Biomedix, Inc. is developing several peptide compounds. Medicis Pharmaceutical Corp. has rights to human derived antimicrobial peptides that may be developed for acne.

In collaboration with Novartis, we are co-developing a humanized antibody to the target CD40, and, at the current time, there are several CD40-related programs under development, mostly focused on the development of CD40 ligand products. For example, SGN-40 is a humanized monoclonal antibody under development by Seattle Genetics, Inc. which is targeting CD40 antigen. Seattle Genetics is currently conducting a phase II clinical trial for patients with diffuse large B-cell lymphoma, the most common type of aggressive non-Hodgkin’s lymphoma, and phase I trials for patients with multiple myeloma or chronic lymphocytic leukemia. In January of 2007, Seattle Genetics entered into an exclusive worldwide license agreement with Genentech to develop and commercialize SGN-40. Under the agreement, Genentech will fund future research, development, manufacturing and commercialization costs. In January of 2007, Kirin Brewery Company, Limited and Astellas Pharma Inc. announced that they have entered into a license and collaborative research and development agreement under which they will exclusively collaborate in developing and marketing a fully human anti-CD40 antagonistic monoclonal antibody worldwide with a first target indication of prophylaxis of organ rejection associated with organ transplantation.

It is possible that other companies may be developing other products based on the same human protein as our NEUPREX^® product, and these products may prove to be more effective than NEUPREX^®. It is also possible that other companies may be developing other products based on the same therapeutic target as our XOMA 052 product and these products may prove to be more effective than XOMA 052.

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Even if we or our third party collaborators or licensees bring products to market, we may be unable to effectively price our products or obtain adequate reimbursement for sales of our products, which would prevent our products from becoming profitable.

If we or our third party collaborators or licensees succeed in bringing our product candidates to the market, they may not be considered cost-effective, and reimbursement to the patient may not be available or may not be sufficient to allow us to sell our products on a competitive basis. In both the United States and elsewhere, sales of medical products and treatments are dependent, in part, on the availability of reimbursement to the patient from third-party payors, such as government and private insurance plans. Third-party payors are increasingly challenging the prices charged for pharmaceutical products and services. Our business is affected by the efforts of government and third-party payors to contain or reduce the cost of health care through various means. In the United States, there have been and will continue to be a number of federal and state proposals to implement government controls on pricing. In addition, the emphasis on managed care in the United States has increased and will continue to increase the pressure on the pricing of pharmaceutical products. We cannot predict whether any legislative or regulatory proposals will be adopted or the effect these proposals or managed care efforts may have on our business.

If we and our partners are unable to protect our intellectual property, in particular our patent protection for our principal products and processes, and prevent its use by third parties, our ability to compete in the market will be harmed, and we may not realize our profit potential.

We rely on patent protection, as well as a combination of copyright, trade secret, and trademark laws to protect our proprietary technology and prevent others from duplicating our products. However, these means may afford only limited protection and may not:

Because of the length of time and the expense associated with bringing new products to the marketplace, we and our partners hold and are in the process of applying for a number of patents in the United States and abroad to protect our products and important processes and also have obtained or have the right to obtain exclusive licenses to certain patents and applications filed by others. However, the mere issuance of a patent is not conclusive as to its validity or its enforceability. The United States Federal Courts or equivalent national courts or patent offices elsewhere may invalidate our patents or find them unenforceable. In addition, the laws of foreign countries may not protect our intellectual property rights effectively or to the same extent as the laws of the United States. If our intellectual property rights are not adequately protected, we may not be able to commercialize our technologies, products, or services, and our competitors could commercialize our technologies, which could result in a decrease in our sales and market share that would harm our business and operating results. Specifically, the patent position of biotechnology companies generally is highly uncertain and involves complex legal and factual questions. The legal standards governing the validity of biotechnology patents are in transition, and current defenses as to issued biotechnology patents may not be adequate in the future. Accordingly, there is uncertainty as to:

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We have established an extensive portfolio of patents and applications, both United States and foreign, related to our BPI-related products, including novel compositions, their manufacture, formulation, assay and use. We have also established a portfolio of patents, both United States and foreign, related to our BCE technology, including claims to novel promoter sequences, secretion signal sequences, compositions and methods for expression and secretion of recombinant proteins from bacteria, including immunoglobulin gene products.

If certain patents issued to others are upheld or if certain patent applications filed by others issue and are upheld, we may require licenses from others in order to develop and commercialize certain potential products incorporating our technology or we may become involved in litigation to determine the proprietary rights of others. These licenses, if required, may not be available on acceptable terms, and any such litigation may be costly and may have other adverse effects on our business, such as inhibiting our ability to compete in the marketplace and absorbing significant management time.

Due to the uncertainties regarding biotechnology patents, we also have relied and will continue to rely upon trade secrets, know-how and continuing technological advancement to develop and maintain our competitive position. All of our employees have signed confidentiality agreements under which they have agreed not to use or disclose any of our proprietary information. Research and development contracts and relationships between us and our scientific consultants and potential customers provide access to aspects of our know-how that are protected generally under confidentiality agreements. These confidentiality agreements may be breached or may not be enforced by a court. To the extent proprietary information is divulged to competitors or to the public generally, such disclosure may adversely affect our ability to develop or commercialize our products by giving others a competitive advantage or by undermining our patent position.

Litigation regarding intellectual property can be costly and expose us to risks of counterclaims against us.

We may be required to engage in litigation or other proceedings to protect our intellectual property. The cost to us of this litigation, even if resolved in our favor, could be substantial. Such litigation could also divert management’s attention and resources. In addition, if this litigation is resolved against us, our patents may be declared invalid, and we could be held liable for significant damages. In addition, we may be subject to a claim that we are infringing another party’s patent. If such claim is resolved against us, we or our collaborators may be enjoined from developing, manufacturing, selling or importing products, processes or services unless we obtain a license from the other party. Such license may not be available on reasonable terms, thus preventing us from using these products, processes or services and adversely affecting our revenue.

Manufacturing risks and inefficiencies may adversely affect our ability to manufacture products for ourselves or others.

We are subject to manufacturing risks which may hinder our ability to provide manufacturing services for our own benefit or to third parties. Additionally, unanticipated fluctuations in customer requirements may lead to manufacturing inefficiencies. We must provide our manufacturing services in compliance with regulatory requirements, in sufficient quantities and on a timely basis, while maintaining acceptable product quality and manufacturing costs. Additional resources and changes in our manufacturing processes may be required for each new product or customer or to meet increasing customer requirements once a contract has been initiated, and this work may not be successfully or efficiently completed.

In addition, the development work and products addressed in new contracts may not share production attributes with our existing projects to the extent we anticipate, and consequently these new contracts may require the development of new manufacturing technologies and expertise. If we are unable to develop manufacturing capabilities as needed, on acceptable terms, our ability to complete these contracts or enter into additional contracts may be adversely affected.

Manufacturing and quality problems may arise in the future as we continue to perform these services for our own benefit and under additional manufacturing contracts. Consequently, our internal development goals or

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milestones under our contracts may not be achieved in a timely manner or at a commercially reasonable cost, or at all. In addition, we continue to make investments to improve our manufacturing processes and to design, develop and purchase manufacturing equipment that may not yield the improvements that we expect. Inefficiencies or constraints related to our manufacturing may adversely affect our overall financial results. Such inefficiencies or constraints may also result in delays or loss of current or potential customers due to their dissatisfaction.

The financial terms of future collaborative or licensing arrangements could result in dilution of our share value.

Funding from collaboration partners and others has in the past and may in the future involve issuance by us of our shares. Because we do not currently have any such arrangements, we cannot be certain how the purchase price of such shares, the relevant market price or premium, if any, will be determined or when such determinations will be made. Any such issuance could result in dilution in the value of our issued and outstanding shares.

Because many of the companies we do business with are also in the biotechnology sector, the volatility of that sector can affect us indirectly as well as directly.

As a biotechnology company that collaborates with other biotech companies, the same factors that affect us directly can also adversely impact us indirectly by affecting the ability of our collaborators, partners and others we do business with to meet their obligations to us and reduce our ability to realize the value of the consideration provided to us by these other companies.

For example, in connection with our licensing transactions relating to our BCE technology, we have in the past and may in the future agree to accept equity securities of the licensee in payment of license fees. The future value of these or any other shares we receive is subject both to market risks affecting our ability to realize the value of these shares and more generally to the business and other risks to which the issuer of these shares may be subject.

As we do more business internationally, we will be subject to additional political, economic and regulatory uncertainties.

We may not be able to successfully operate in any foreign market. We believe that, because the pharmaceutical industry is global in nature, international activities will be a significant part of our future business activities and that, when and if we are able to generate income, a substantial portion of that income will be derived from product sales and other activities outside the United States. Foreign regulatory agencies often establish standards different from those in the United States, and an inability to obtain foreign regulatory approvals on a timely basis could put us at a competitive disadvantage or make it uneconomical to proceed with a product’s development. International operations and sales may be limited or disrupted by:

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Because we are a relatively small biopharmaceutical company with limited resources, we may not be able to attract and retain qualified personnel, and the loss of key personnel could delay or prevent achieving our objectives.

Our success in developing marketable products and achieving a competitive position will depend, in part, on our ability to attract and retain qualified scientific and management personnel, particularly in areas requiring specific technical, scientific or medical expertise. There is intense competition for such personnel. Our research, product development and business efforts could be adversely affected by the loss of one or more key members of our scientific or management staff, particularly our executive officers: John L. Castello, our Chairman of the Board, President and Chief Executive Officer; J. David Boyle II, our Vice President, Finance and Chief Financial Officer; Patrick J. Scannon, M.D., Ph.D., our Executive Vice President and Chief Biotechnology Officer; and Christopher J. Margolin, our Vice President, General Counsel and Secretary. We currently have no key person insurance on any of our employees. In February of 2007, Mr. Castello announced his plans to retire. Although he intends to continue to serve in his present capacities during the candidate search and transition period, our business could be adversely affected if the search and transition period take longer than expected or we are unable to find a suitable replacement.

We had approximately 256 employees as of December 31, 2006, and we anticipate that we will require additional experienced executive, accounting, research and development, legal, administrative and other personnel in the future. There is intense competition for the services of these personnel, especially in California. Moreover, we expect that the high cost of living in the San Francisco Bay Area, where our headquarters and manufacturing facilities are located, may impair our ability to attract and retain employees in the future. If we do not succeed in attracting new personnel and retaining and motivating existing personnel, our operations may suffer and we may be unable to implement our current initiatives or grow effectively.

Calamities, power shortages or power interruptions at our Berkeley headquarters and manufacturing facility could disrupt our business and adversely affect our operations, and could disrupt the businesses of our customers.

Our principal operations are located in Northern California, including our corporate headquarters and manufacturing facility in Berkeley, California. In addition, many of our collaborators and licensees are located in California. All of these locations are in areas of seismic activity near active earthquake faults. Any earthquake, terrorist attack, fire, power shortage or other calamity affecting our facilities or our customers’ facilities may disrupt our business and could have material adverse effect on our business and results of operations.

We are exposed to an increased risk of product liability claims.

The testing, marketing and sales of medical products entails an inherent risk of allegations of product liability. In the event of one or more large, unforeseen awards of damages against us, our product liability insurance may not provide adequate coverage. A significant product liability claim for which we were not covered by insurance would have to be paid from cash or other assets. To the extent we have sufficient insurance coverage, such a claim would result in higher subsequent insurance rates. In addition, product liability claims can have various other ramifications including loss of future sales opportunities, increased costs associated with replacing products, and a negative impact on our goodwill and reputation, which could also adversely affect our business and operating results.

We may be subject to increased risks because we are a Bermuda company.

Alleged abuses by certain companies that have changed their legal domicile from jurisdictions within the United States to Bermuda have created an environment where, notwithstanding that we changed our legal domicile in a transaction that was approved by our shareholders and fully taxable to our company under United States law, we may be exposed to various prejudicial actions, including:

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We do not know whether any of these things will happen, but if implemented one or more of them may have an adverse impact on our future operations or our share price.

If you were to obtain a judgment against us, it may be difficult to enforce against us because we are a foreign entity.

We are a Bermuda company. All or a substantial portion of our assets, including substantially all of our intellectual property, may be located outside the United States. As a result, it may be difficult for shareholders and others to enforce in United States courts judgments obtained against us. We have irrevocably agreed that we may be served with process with respect to actions based on offers and sales of securities made hereby in the United States by serving Christopher J. Margolin, c/o XOMA Ltd., 2910 Seventh Street, Berkeley, California 94710, our United States agent appointed for that purpose. Uncertainty exists as to whether Bermuda courts would enforce judgments of United States courts obtained in actions against us or our directors and officers that are predicated upon the civil liability provisions of the United States securities laws or entertain original actions brought in Bermuda against us or such persons predicated upon the United States securities laws. There is no treaty in effect between the United States and Bermuda providing for such enforcement, and there are grounds upon which Bermuda courts may not enforce judgments of United States courts. Certain remedies available under the United States federal securities laws may not be allowed in Bermuda courts as contrary to that nation’s policy.

Our shareholder rights agreement or bye-laws may prevent transactions that could be beneficial to our shareholders and may insulate our management from removal.

In February of 2003, we adopted a new shareholder rights agreement (to replace the shareholder rights agreement that had expired), which could make it considerably more difficult or costly for a person or group to acquire control of us in a transaction that our board of directors opposes.

Our bye-laws:

These provisions of our shareholders rights agreement and our bye-laws, alone or in combination with each other, may discourage transactions involving actual or potential changes of control, including transactions that otherwise could involve payment of a premium over prevailing market prices to holders of common shares, could limit the ability of shareholders to approve transactions that they may deem to be in their best interests, and could make it considerably more difficult for a potential acquirer to replace management.

We may issue additional equity securities and thereby materially and adversely affect the price of our common shares.

We are authorized to issue, without shareholder approval, 1,000,000 preference shares, of which 2,959 were issued and outstanding as of December 31, 2006, which may give other shareholders dividend, conversion,

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voting, and liquidation rights, among other rights, which may be superior to the rights of holders of our common shares. In addition, we are authorized to issue, without shareholder approval, up to 210,000,000 common shares, of which 105,454,389 were issued and outstanding as of December 31, 2006. If we issue additional equity securities, the price of our common shares and, in turn, the price of our convertible notes may be materially and adversely affected. In addition, as of December 31, 2006, there were $44.5 million aggregate principal amount of New Notes outstanding, which were convertible into an aggregate of 23,750,873 common shares, with an aggregate of 1,889,317 additional shares issuable in lieu of the additional interest that would be due on such conversion.

If the trading price of our common shares fails to comply with the continued listing requirements of The Nasdaq National Market, we would face possible delisting, which would result in a limited public market for our common shares and make obtaining future debt or equity financing more difficult for us.

If we do not continue to comply with the continued listing requirements for The Nasdaq National Market, then Nasdaq may provide written notification regarding the delisting of our securities. At that time, we would have the right to request a hearing to appeal The Nasdaq determination and would also have the option to apply to transfer our securities to The Nasdaq SmallCap Market.

We cannot be sure that our price will comply with the requirements for continued listing of our common shares on The Nasdaq National Market, or that any appeal of a decision to delist our common shares will be successful. If our common shares lose their status on The Nasdaq National Market and we are not successful in obtaining a listing on The Nasdaq SmallCap Market, our common shares would likely trade in the over-the-counter market.

If our common shares are neither listed for trading on a United States national or regional securities exchange nor approved for trading on The Nasdaq National Market, Nasdaq SmallCap Market or any other established United States system of automated dissemination or quotations of securities prices, it would be deemed a “fundamental change” under the indenture governing our convertible notes, giving the holders thereof the right to require us to repurchase such notes. Our failure to repurchase our convertible notes would constitute an event of default under the notes indenture, which might constitute an event of default under the terms of our other debt.

If our shares were to trade on the over-the-counter market, selling our common shares could be more difficult because smaller quantities of shares would likely be bought and sold, transactions could be delayed, and security analysts’ coverage of us may be reduced. In addition, in the event our common shares are delisted, broker-dealers have certain regulatory burdens imposed upon them, which may discourage broker-dealers from effecting transactions in our common shares, further limiting the liquidity thereof. These factors could result in lower prices and larger spreads in the bid and ask prices for common shares.

Such delisting from The Nasdaq National Market or future declines in our share price could also greatly impair our ability to raise additional necessary capital through equity or debt financing, and could significantly increase the ownership dilution to shareholders caused by our issuing equity in financing or other transactions. Consent under the Exchange Control Act 1972 (and its related regulations) has been obtained from the Bermuda Monetary Authority for the issue and transfer of our shares, notes and other securities to and between non-residents of Bermuda for exchange control purposes, but this consent is conditional on our shares remaining listed on an appointed stock exchange. We cannot assure you that the Bermuda Monetary Authority will give the same or a similar consent in the event our common shares are no longer listed on The Nasdaq National Market or another appointed stock exchange. In the absence of such a general consent, specific consents of the Bermuda Monetary Authority would be required for certain issues and transfers of our shares, notes and other securities.

None.

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Our development and manufacturing facilities are located in Berkeley and Emeryville, California. We lease approximately 135,000 square feet of space including approximately 35,000 square feet of research and development laboratories, 56,000 square feet of production and production support facilities and 44,000 square feet of office space. A separate 17,000 square foot technology development and pilot facility is owned by us.

We produced multiple anti-botulinum neurotoxin antibodies and XOMA 052 in addition to performing numerous small-scale development runs in 2006. We have previously produced MLN2222, TPO mimetic antibody, NEUPREX^®, RAPTIVA^®, MLN2201 and ING-1 for clinical trials and other testing needs at our Berkeley manufacturing facilities, pursuant to a drug manufacturing license obtained from the State of California. We recently received Investigational Medicinal Products (IMP) Certification from the Medicines and Healthcare Products Regulatory Agency of the United Kingdom to allow production of clinical trial materials for use in the European Union. We base our manufacturing capability on recombinant DNA technology, which can produce therapeutic products from either mammalian or microbial cells. Our primary manufacturing facility houses three fermentation trains with a tank size of 2,750 liters. Our Pilot Plant houses two fermentation trains with a tank size of 500 liters. Each facility has associated isolation and purification equipment within production suites. We perform our own formulation and contract with third parties for final sterile filling and finishing.

In September of 2004, XOMA (US) LLC entered into a collaboration with Aphton for the treatment of gastrointestinal and other gastrin-sensitive cancers using anti-gastrin monoclonal antibodies. In May of 2006, Aphton filed for bankruptcy protection under Chapter 11, Title 11 of the United States Bankruptcy Code in the United States Bankruptcy Court for the District of Delaware, No. 06-10510 (CSS). XOMA (US) LLC filed a proof of claim in the proceeding, as an unsecured creditor of Aphton, for approximately $594,000. Recently, Aphton and the Official Committee of Unsecured Creditors filed a Proposed Plan of Reorganization that would result in a liquidation of Aphton and the process of seeking approval of that Plan has commenced. It is not presently known what, if any, distributions will be made to holders of unsecured claims.

No matters were brought to a vote of our shareholders in the quarter ended December 31, 2006.

Executive Officers

Our executive officers and their respective ages, as of December 31, 2006, and positions are as follows:

The Board of Directors elects all officers annually. There is no family relationship between or among any of the officers or directors.

Business Experience

Mr. Castello became Chairman of the Board, President and Chief Executive Officer in March of 1993. From April of 1992 to March of 1993, Mr. Castello was President, Chief Executive Officer and a director.

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Mr. Castello was President and Chief Operating Officer of the Ares-Serono Group from 1988 to 1991 and prior to that was President of the Serono Diagnostics Division from 1986 to 1988. Ares-Serono Group is known in the United States for fertility drugs and it is also the manufacturer of a bioengineered human growth hormone which is marketed primarily outside of the United States. Mr. Castello previously held senior management positions at Amersham International plc and Abbott Laboratories. Mr. Castello is also a director of Cholestech Corporation, which is engaged in the business of developing products for the diagnostic measurement of cholesterol and other blood components.

Dr. Scannon is one of our founders and has served as a director since our formation. Dr. Scannon became Executive Vice President and Chief Biotechnology Officer in May of 2006. Previously he was our Chief Scientific and Medical Officer beginning in March of 1993, served as our as Vice Chairman, Scientific and Medical Affairs from April of 1992 to March of 1993 and our President from our formation until April of 1992. From 1998 until 2001, Dr. Scannon served as a director of NanoLogics, Inc., a software company. From 1979 until 1981, Dr. Scannon was a clinical research scientist at the Letterman Army Institute of Research in San Francisco. A Board-certified internist, Dr. Scannon holds a Ph.D. in organic chemistry from the University of California, Berkeley and an M.D. from the Medical College of Georgia.

Mr. Boyle is our Vice President, Finance and Chief Financial Officer. Before joining us in January 2005, he was Vice President, Finance for Polycom, Inc. From 1996 to 1999, he served as Executive Vice President and Chief Financial Officer of Salix Pharmaceuticals Ltd. Before joining Salix, Mr. Boyle spent five years with Serono, S.A. in Switzerland and the United States, most recently as Vice President, Finance and Administration for North America.

Mr. Margolin is our Vice President, General Counsel and Secretary. Prior to joining us in 1991, Mr. Margolin was a corporate attorney holding several different executive legal positions for Raychem Corporation, an international high technology company, for 11 years. From 1975 to 1980, he was a division counsel for TRW Inc. and from 1972 to 1975, he was an associate at the law firm of McCutchen, Black, Verleger and Shea in Los Angeles.

PART II

Our common shares trade on the Nasdaq National Market under the symbol “XOMA.” The following table sets forth the quarterly range of high and low reported sale prices of our common shares on the Nasdaq National Market for the periods indicated.

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On March 5, 2007, there were approximately 2,764 shareholders of record of our common shares, one of which is Cede & Co., a nominee for Depository Trust Company (“DTC”). All of the common shares held by brokerage firms, banks and other financial institutions as nominees for beneficial owners are deposited into participant accounts at DTC and are therefore considered to be held of record by Cede & Co. as one shareholder.

We have not paid dividends on our common shares. We currently intend to retain any earnings for use in the development and expansion of our business. We, therefore, do not anticipate paying cash dividends on our common shares in the foreseeable future (see Note 5, “Share Capital,” to the Consolidated Financial Statements.).

In July of 2004, we exercised an option to sell 920,284 shares to Millennium for gross proceeds of $3.7 million or $3.99 per share. In November of 2003, we exercised an option to sell 763,719 shares to Millennium for gross proceeds of $5.4 million or $7.07 per share. In June of 2003, we exercised an option to sell 608,766 shares to Millennium for gross proceeds of $4.0 million or $6.57 per share. In December of 2002, we issued 1,443,418 shares to Millennium for gross proceeds of $7.5 million or $5.20 per share. These sales of common shares to Millennium were exempt from registration under the Securities Act pursuant to Section 4(2) thereof. In October of 2004, the investment agreement with Millennium was terminated and there will be no further issuance of common shares to Millennium under this agreement.

In December of 2003, we issued 2,959 of Series B preferred shares to Genentech in repayment of the $29.6 million outstanding balance under the convertible subordinated debt agreement. These shares are convertible into approximately 3.8 million common shares, which represents a price of $7.75 per share.

In February of 2005, we issued $60.0 million of 6.5% convertible senior notes due in 2012, the proceeds of which are being used for general corporate purposes, including current research and development projects, the development of new products or technologies, equipment acquisitions, general working capital purposes and operating expenses. The notes were initially convertible into approximately 32 million common shares at a conversion rate of 533.4756 of our common shares per $1,000 principal amount of notes, which is equivalent to a conversion price of approximately $1.87 per common share. Before February 6, 2008, we could not have redeemed the notes. On or after February 6, 2008, we could have redeemed any or all of the notes at 100% of the principal amount, plus accrued and unpaid interest, if our common shares traded at 150% of the conversion price then in effect for 20 trading days in a 30 consecutive trading day period. Holders of the notes could have required us to repurchase some or all of the notes for cash at a repurchase price equal to 100% of the principal amount of the notes plus accrued and unpaid interest following a fundamental change. In addition, following certain fundamental changes, we would have increased the conversion rate by a number of additional common shares or, in lieu thereof, we could have, in certain circumstances, elected to adjust the conversion rate and related conversion obligation so that the notes would have been convertible into shares of the acquiring, continuing or surviving company. The convertible senior notes were issued, to the initial purchasers, for net proceeds of $56.6 million. The issuance costs of approximately $3.4 million are being amortized on a straight-line basis over the 84 month life of the notes.

In February of 2006, we completed an exchange offer with holders of our 6.5% convertible senior notes due 2012 in which we exchanged $60.0 million aggregate principal amount of our new 6.5% Convertible SNAPs_SM due 2012 (the “New Notes”) for all $60.0 million aggregate principal amount of our then outstanding convertible senior notes due 2012. We also issued an additional $12.0 million of New Notes to the public for cash at a public offering price of 104% of principal, or $12.5 million. The New Notes are initially convertible into approximately 38.4 million common shares at a conversion rate of 533.4756 of common shares per $1,000 principal amount of New Notes, which is equivalent to a conversion price of approximately $1.87 per common share. Before February 10, 2010, we may not redeem the New Notes. On or after February 10, 2010, we may redeem any or all of the New Notes at 100% of the principal amount, plus accrued and unpaid interest. In addition, we may automatically convert some or all of the New Notes on or prior to the maturity date if the closing price of our common shares has exceeded 150% of the conversion price then in effect for at least 20 trading days during any

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consecutive 30 trading day period ending within five trading days prior to the notice of auto-conversion. If we elect to automatically convert, or if holders elect to voluntarily convert, some or all of the New Notes on or prior to February 10, 2010, we must pay or provide for additional interest equal to four years’ worth of interest less any interest paid or provided for, on the principal amount so converted, prior to the date of conversion. Additional interest, if any, shall be paid in cash or, solely at our option and subject to certain limitations, in our common shares valued at the conversion price then in effect.

For the year ended December 31, 2006, $27.5 million of New Notes were converted into 18,262,264 common shares including 3,602,879 shares related to the additional interest payment feature of the notes.

As of March 7, 2007, an additional $42.0 million of our New Notes were converted into 24,223,414 common shares including 1,790,759 shares related to the additional interest payment feature of the notes.

On March 7, 2006, we announced that the conditions necessary for the auto-conversion of the remaining $2.5 million principal outstanding of our convertible debt had been met and that we had elected to notify note holders of our intention to redeem any notes not converted and still outstanding as of March 27, 2007.

The section labeled “Plan-Based Awards” appearing in our proxy statement for the 2007 Annual General Meeting of Shareholders is incorporated herein by reference.

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The following table contains our selected financial information including statement of operations and balance sheet data for the years 2002 through 2006. The selected financial information has been derived from our audited consolidated financial statements. The selected financial information should be read in conjunction with the consolidated financial statements and notes thereto included in Item 8 of this report and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included in Item 7 below. The data set forth below is not necessarily indicative of the results of future operations.

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Quarterly Results of Operations (Unaudited)

The following is a summary of the quarterly results of operations for the years ended December 31, 2006 and 2005.

Overview

We are a biopharmaceutical company that discovers, develops and manufactures antibodies and other genetically-engineered protein products to treat immunological and inflammatory disorders, cancer and infectious diseases.

In the near term, our ability to achieve profitability will be highly dependent on sales levels of RAPTIVA^®, which we developed under a collaboration agreement with Genentech, and LUCENTIS^® for which Genentech licensed our BCE technology. Genentech is responsible for the manufacturing, marketing and sales effort in support of these products and we are entitled to receive royalties on worldwide sales. RAPTIVA^® has been approved in the United States and the European Union for treating patients suffering from moderate-to-severe plaque psoriasis. LUCENTIS^® is approved in the United States and Europe and is a treatment for neovascular (wet) age-related macular degeneration. Our near-term profits will also be influenced by our ability to generate

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revenues or benefit from cost-sharing arrangements, funded research and development, contract manufacturing or other development activities. We are developing a number of products, both proprietary and under collaboration agreements with other companies and may enter into additional arrangements. Our objective in development collaborations is to leverage our existing development infrastructure to broaden and strengthen our new product pipeline beyond what we can accomplish with proprietary products, thereby diversifying our development risk and gaining financial support from our collaboration partners.

We incurred a net loss in two of the past three years and expect to continue to operate at a loss until sufficient profits are generated from RAPTIVA^®, LUCENTIS^® and various manufacturing and development arrangements, or until we achieve additional regulatory approvals and commence commercial sales of additional products. The timing and likelihood of additional approvals is uncertain and there can be no assurance that approvals will be granted or that revenues from product sales will be sufficient to attain profitability.

Critical Accounting Policies and the Use of Estimates

The accompanying discussion and analysis of our financial condition and results of operations are based upon our consolidated financial statements and the related disclosures, which have been prepared in accordance with accounting principles generally accepted in the United States. The preparation of these financial statements requires us to make estimates, assumptions and judgments that affect the reported amounts in our consolidated financial statements and accompanying notes. On an on-going basis, we evaluate our estimates, including those related to terms of research collaborations, investments, share compensation, impairment issues and the estimated useful life of assets and contingencies. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions.

We believe the following policies to be the most critical to an understanding of our financial condition and results of operations because they require us to make estimates, assumptions and judgments about matters that are inherently uncertain.

Revenue Recognition

Revenue is generally recognized when the four basic criteria of revenue recognition are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the fee is fixed and determinable; and (4) collectibility is reasonably assured. Determination of criteria (3) and (4) is based on management’s judgments regarding the nature of the fee charged for products or services delivered and the collectibility of those fees.

We recognize revenue from license and collaboration arrangements, contract services, product sales and royalties. Our revenue arrangements with multiple elements are divided into separate units of accounting, if certain criteria are met, including whether the delivered element has stand-alone value to the customer and whether there is objective and reliable evidence of the fair value of the undelivered items. The consideration we receive is allocated among the separate units based on their respective fair values and the applicable revenue recognition criteria are applied to each of the separate units. Advance payments received in excess of amounts earned are classified as deferred revenue until earned.

License and Collaborative Fees

Revenue from non-refundable license or technology access payments under license and collaborative agreements where we have a continuing obligation to perform is recognized as revenue over the expected period of the continuing performance obligation. We estimate the performance period at the inception of the arrangement and reevaluate it each reporting period. This reevaluation may shorten or lengthen the period over which the remaining revenue is recognized.

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Milestone payments under collaborative arrangements are recognized as revenue upon completion of the milestone events, which represent the culmination of the earnings process because we have no future performance obligations related to the payment. Milestone payments that require a continuing performance obligation on our part are recognized over the expected period of the continuing performance obligation. Amounts received in advance are recorded as deferred revenue until the related milestone is completed. Allowances are established for estimated uncollectible amounts, if any.

Contract Revenue

Contract revenue for research and development involves our providing research and development for manufacturing processes to collaborative partners or others. Revenues for certain contracts are accounted for by a proportional performance, or output based, method where performance is based on agreed progress toward elements defined in the contract. We recognize revenue under these arrangements as the related research and development costs are incurred and collectibility is reasonably assured. Any cumulative impact of a change in an estimate of a contract revenue or cost is recorded in the period in which the change becomes known.

Royalty Revenue

Royalty revenue and royalty receivables are generally recorded in the periods these royalties are earned, in advance of collection. The royalty revenue and receivables in these instances are based upon communication with collaborative partners, historical information and forecasted sales trends. Under some of our agreements with licensees that include receipt of royalty revenue, we do not have sufficient historical information to estimate royalty revenues or receivables in the period that these royalties are earned. For these contracts, we record royalty revenue upon cash receipt.

Research and Development Expenses

We expense research and development expense as incurred. Research and development expenses consist of direct and research-related allocated overhead costs such as facilities costs, salaries and related personnel costs, patent costs and material and supply costs. In addition, research and development expenses include costs related to clinical trials to validate our testing processes and procedures and related overhead expenses. Under cost sharing arrangements with collaborative partners, differences between our actual research and development spending and our share of such spending under the collaboration agreement will also be included as a cost sharing adjustment in our research and development expense. Expenses resulting from clinical trials are recorded when incurred based in part on estimates as to the status of the various trials. From time to time, research and development expenses may include upfront fees and milestones paid to collaborative partners for the purchase of rights to in-process research and development. Such amounts are expensed as incurred. The timing of upfront fees and milestone payments in the future may cause variability in our future research and development expenses.

Long-Lived Assets

In accordance with Financial Accounting Standards Board (“FASB”) Statement No. 144, “Accounting for the Impairment or Disposal of Long-Lived Assets” which superseded FASB Statement No. 121, “Accounting for the Impairment of Long-Lived Assets and for Long-Lived Assets to be Disposed of,” we record impairment losses on long-lived assets used in operations when events and circumstances indicate that the assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amounts of those assets.

Share Based Compensation

On January 1, 2006, we adopted SFAS 123R, which requires the measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors, including

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employee share options and employee share purchases related to the Employee Share Purchase Plan, on estimated fair values. We are using the modified prospective method. Under this method, we are required to record compensation expense for all awards granted after the date of adoption and for the unvested portion of previously granted awards that remain outstanding at the date of adoption. To estimate the value of an award, we use the Black-Scholes option pricing model. This model requires inputs such as expected life, expected volatility and risk-free interest rate. Further, the forfeiture rate also impacts the amount of aggregate compensation. These inputs are subjective and generally require significant analysis and judgment to develop. While estimates of expected life, volatility and forfeiture rate are derived primarily from our historical data, the risk-free rate is based on the yield available on United States Treasury zero-coupon issues. We review our valuation assumptions quarterly and, as a result, it is likely we will change our valuation assumptions used to value share based awards granted in future periods.

Results of Operations

Revenues

Total revenues in 2006 were $29.5 million, compared with $18.7 million in 2005 and $3.7 million in 2004.

License and collaborative fees revenues in 2006 were $2.8 million, compared with $5.1 million in 2005 and $3.6 million in 2004. These revenues include upfront and milestone payments related to the outlicensing of our products and technologies and other collaborative arrangements. The $2.3 million decrease for the 2006 compared with 2005 and the $1.5 million increase in 2005 compared with 2004 was primarily related to an outlicensing agreement with Merck & Co., Inc. which we recognized in 2005.

Contract and other revenues were $16.3 million in 2006, as compared with $7.4 million in 2005 and zero in 2004. The increase of $8.9 million for 2006, partially resulted from contracts entered into in 2006 with SPRI, Taligen, Cubist, AVEO and, to a lesser extent, other 2006 contracts but was primarily caused by contract manufacturing process services performed under our contracts with NIAID entered into in March of 2005 and July of 2006. The increase from these contracts was partially offset by a reduction in clinical trial services performed on behalf of Genentech and Novartis in 2005.

The March 2005 NIAID contract work was being performed over an eighteen month period. We recognized revenue over the life of the contract as the services were performed on a proportional performance basis and, as per the terms of the contract, a 10% retention on all revenue was being deferred and classified as a receivable until final acceptance of the contract which was achieved in October of 2006. During 2006 and 2005, respectively, we recorded revenues of $9.8 million and $5.2 million from this contract. The July 2006 NIAID contract work is being performed on a cost plus fixed fee basis, per the terms of the contract, over a three year period. We are recognizing revenue as the services are performed on a proportional performance basis.

We defer revenue until all requirements under our revenue recognition policy are met. In 2006, we deferred $26.6 million of revenue from eight contracts including SPRI, NIAID, Takeda and Taligen and recognized $16.1 million in revenue from the eight contracts in addition to the amortization of the $10.0 million in upfront payments received from Novartis for our February 2004 oncology collaboration contract. The Novartis payments are being recognized as revenue over the five year expected term of the agreement. The 2005 $8.3 million beginning balance is the unamortized balance on the Novartis contract, the $1.5 million of revenue deferred relates to NIAID and the $2.0 million of revenue recognized is the Novartis amortization. The 2004 activity relates to the $10.0 million in upfront payments received from Novartis.

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The following table shows the activity in deferred revenue for the years ended December 31, 2006, 2005 and 2004, (in thousands):

The $18.4 million balance in deferred revenue at December 31, 2006, is expected to be recognized as revenue over the next four years. Future amounts may also be impacted by additional consideration received, if any, under existing or any future licensing or other collaborative arrangements.

Revenues from royalties were $10.3 million in 2006, as compared with $6.2 million in 2005 and $0.1 million in 2004. The increase in royalty revenues from 2004 through 2006 resulted primarily from an increase in RAPTIVA^® royalties and the inception of LUCENTIS^® royalties, in June of 2006, earned under our royalty arrangements with Genentech.

Revenues for 2007 are expected to continue to increase as a result of royalties generated by worldwide sales of RAPTIVA^® and LUCENTIS^®, the expected inception of CIMZIA^™ royalties and our existing and additional antibody discovery, manufacturing service and license arrangements.

Research and Development Expenses

Generally speaking, biopharmaceutical development includes a series of steps, including in vitro and in vivo preclinical testing, and Phase I, II and III clinical studies in humans. Each of these steps is typically more expensive than the previous step, but actual timing and the cost to us depends on the product being tested, the nature of the potential disease indication and the terms of any collaborative arrangements with other companies. After successful conclusion of all of these steps, regulatory filings for approval to market the products must be completed, including approval of manufacturing processes and facilities for the product. Our research and development expenses currently include costs of personnel, supplies, facilities and equipment, consultants, patent expenses and third party costs related to preclinical and clinical testing.

In 2006, our research and development expenses were $52.1 million, compared with $39.9 million in 2005 and $49.8 million in 2004.

The $12.2 million increase in 2006 compared with 2005 primarily reflects increases in spending on our contracts with NIAID, Taligen and AVEO, our development of XOMA 052 and NEUPREX^®, and our collaborations with SPRI and Lexicon, partially offset by decreased spending on our collaboration agreements with Novartis, Genentech, Aphton and Millennium, our development of XOMA 629 and the termination of our agreement with Cubist. In addition, during 2006, we recorded $0.5 million of share-based compensation expense. No share based compensation expense was recorded in 2005.

The $9.9 million decrease in 2005 compared with 2004 primarily reflects reduced spending on MLN2222 due to the discontinuation of the Millennium collaboration announced in October 2004, reduced spending on TPO Mimetic due to the termination of the Alexion collaboration in the second quarter of 2005, reduced spending on RAPTIVA^® following the restructuring of our collaboration arrangement with Genentech in January 2005, as well as reduced spending on XMP.629 and other proprietary new product developments through the year. These reductions were partially offset by increased spending on our collaboration agreements with Novartis, Aphton and Lexicon, our research and development work for NIAID, and our internal development of XOMA 052.

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During 2005, we completed an annual review of leasehold improvements. Based on our review, we decided to abandon our plan to add a fermentation unit to our existing research and development facility. As certain leasehold improvements related to this project no longer prolonged the life of the related building nor enhanced its functional use, we expensed approximately $0.6 million to depreciation expense for research and development in December 2005.

Our research and development activities can be divided into earlier stage programs, which include molecular biology, process development, pilot-scale production and preclinical testing, and later stage programs, which include clinical testing, regulatory affairs and manufacturing clinical supplies. Using the current costing methods, the costs associated with these programs approximate the following (in thousands):

Our research and development activities can also be divided into those related to our internal projects and those projects related to collaborative arrangements. The costs related to internal projects versus collaborative arrangements approximate the following (in thousands):

In 2006, three development programs (Novartis, NIAID and XOMA 052) each individually accounted for more than 10% but less than 20%, and no development program accounted for more than 20% of our total research and development expenses. In 2005, one development program (Novartis) accounted for more than 30% but less than 40% and no development program accounted for more than 40% of our total research and development expenses. In 2004, two development programs (XMP.629 and MLN2222) each individually accounted for more than 10% but less than 20% and no development program accounted for more than 20% of our total research and development expenses.

We currently anticipate that research and development expenses will continue to increase in 2007 as compared with 2006. We expect our spending on our oncology collaboration with Novartis and Lexicon to continue as well as increases in spending on our collaborations with SPRI and Takeda, our contracts with NIAID, Taligen and AVEO, our development of XOMA 052, NEUPREX^® and XOMA 629 and other new projects. Future research and development spending may also be impacted by potential new licensing or collaboration arrangements, as well as the termination of existing agreements. Beyond this, the scope and magnitude of future research and development expenses are difficult to predict at this time.

General and Administrative Expenses

General and administrative expenses include salaries and related personnel costs, facilities costs and professional fees. In 2006, general and administrative expenses were $18.1 million compared with $14.8 million in 2005 and $15.6 million in 2004.

The increase of $3.3 million for 2006 compared with 2005 resulted primarily from increased employee related costs, principally from additional legal and business development staffing, debt issuance expenses related

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to our February 2006 convertible debt, and increased legal, audit and other consulting fees. In addition, during 2006, we recorded $0.5 million of share-based compensation expense. No share-based compensation expense was recorded in 2005.

The decrease of $0.8 million in 2005 compared with 2004 resulted from lower accounting fees related to the first year implementation of Sarbanes-Oxley in 2004, partially offset by fees related to our convertible debt exchange which was completed in 2006.

We anticipate that general and administrative expenses will remain flat in 2007 as a result of a reduction in outside professional fees offset by an increase in salaries and other personnel-related costs.

Collaborative Arrangement Expenses

Collaborative arrangement expenses, which related exclusively to RAPTIVA^®, were zero in 2006 and 2005. In 2004, collaborative arrangement expenses were $16.4 million which reflects our 25% share of commercialization costs for RAPTIVA^® in excess of Genentech’s revenues less cost of goods sold, research and development cost sharing adjustments and royalties on sales outside the United States. Because of the restructuring of our arrangement with Genentech, which was effective January 1, 2005, we are no longer responsible for a share of operating costs or research and development expenses, but rather we are entitled to receive royalties on RAPTIVA^®’s worldwide sales. Genentech is responsible for all development costs and, to the extent that we provide further clinical trial support or other development services for RAPTIVA^®, we will be compensated by Genentech. The 2004 collaborative arrangement expenses are as follow (in thousands):

In addition to the amounts shown in the above table, we incurred research and development expenses on RAPTIVA^® of zero, $1.0 million and $3.9 million in 2006, 2005 and 2004, respectively.

Investment and Interest Income

In 2006, investment and interest income was $1.7 million compared with $1.9 million in 2005 and $0.5 million in 2004. Investment and interest income consists primarily of interest earned on our cash and investment balances. The decrease in 2006 compared with 2005 resulted from lower average cash balances partially offset by higher interest rates. The increase in 2005 compared with 2004 resulted from higher average cash balances due to the $60.0 million raised in a debt financing at the beginning of 2005, as well as higher interest rates and realized gains on sale of equity investments during the year. Investment and interest income is expected to decrease in 2007 due to lower cash investment balances.

We review our investments for other-than-temporary impairment whenever the value of the investment is less than the amortized cost. As of December 31, 2006, five investments with an aggregate fair value of approximately $3.8 million, had aggregate unrealized losses of $11,000, compared with 18 investments with an aggregate fair value of approximately $14.5 million with aggregate unrealized losses of $69,000 at December 31, 2005. The unrealized losses were recorded in other comprehensive income. All such investments have been or were in an unrealized loss position for, and have holding periods of, less than twelve months. We have not previously sold similar investments at a loss, and we currently have the financial ability to hold short-term investments with an unrealized loss until maturity and not incur any recognized losses. As a result, we do not believe any unrealized losses represent an other-than-temporary impairment.

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Interest Expense

In 2006, interest expense was $12.9 million compared with $4.3 million in 2005 and $1.2 million in 2004. Interest expense for 2006, consists of $6.9 million from the revaluation, to fair market value, of the embedded derivative on our convertible debt, including $4.8 million related to shares paid for the additional interest feature on converted debt, $3.4 million of interest expense payable on our convertible debt, $1.0 million in net amortization of debt issuance costs, discount and premium on our convertible debt, $0.5 million of interest payable on our term loan, $42,000 in amortization of debt issuance costs on our term loan and $1.0 million of interest payable on our note with Novartis. Interest expense for 2005 consisted of $3.5 million of interest on our convertible debt, $0.5 million in amortization of debt issuance costs on our convertible debt and $0.3 million of interest payable on our note with Novartis. Interest expense for 2004 consisted primarily of interest on the convertible notes due to Genentech and Millennium. Interest expense is expected to slightly decrease in 2007 as a result of the conversion of our convertible debt partially offset by increased interest on our term loan and Novartis loan facility.

Other Income (Expense)

In 2006, other income (expense) was $0.1 million compared with $41.2 million in 2005 and $(0.1) million in 2004. The 2005 income amount primarily reflects a one-time gain of $40.9 million as a result of the restructuring of the Genentech agreement in January of 2005.

Income Taxes

We have recorded cumulative net deferred tax assets of $163.3 million and $157.4 million at December 31, 2006 and 2005, respectively, principally attributable to the timing of the deduction of certain expenses associated with certain research and development expenses, net operating loss and other carryforwards. We also recorded corresponding valuation allowances of $163.3 million and $157.4 million at December 31, 2006 and 2005, respectively, to offset these deferred tax assets, as management cannot predict with reasonable certainty that the deferred tax assets to which the valuation allowance relates will be realized.

As of December 31, 2006, we had federal net operating loss carryforwards of approximately $173.5 million to offset future taxable income. We also had federal research and development tax credit carryforwards of approximately $11.3 million. If not utilized, these carryforwards will begin to expire in 2006. The availability of our net operating loss and tax credit carryforwards may be subject to substantial limitation if it is determined that our ownership has changed by more than 50% over a three year period.

In 2006, income tax expense was zero compared with $3,000 in 2005 and zero in 2004, the expense in 2005 is related to activities of our foreign operations.

Accounting for Share-Based Compensation

Prior to the adoption of Financial Accounting Standards No. 123 (revised 2004), “Share-Based Payment” (“SFAS 123R”) on January, 1, 2006, we accounted for our share-based compensation plans under the intrinsic value method described in Accounting Principles Board Opinion No. 25, “Accounting for Stock Issued to Employees,” (“APB 25”) and related Interpretations as permitted by Financial Accounting Standards No. 123, “Accounting for Stock-Based Compensation” (“SFAS 123”), as amended by Financial Accounting Standards No. 148, “Accounting for Stock-Based Compensation—Transition and Disclosure” (“SFAS 148”). In general, as the exercise price of the options granted under our plans was equal to the market price of the underlying common shares on the grant date, no share-based employee compensation cost was recognized. As required by SFAS 148 prior to the adoption of SFAS 123R, we provided pro forma net income (loss) and pro forma net income (loss) per common share disclosures for share-based awards, as if SFAS 123 had been applied.

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SFAS 123R requires all share based payments to be recognized in the financial statements based on their fair values. We are using the modified prospective method. Under this method, compensation cost recognized during the year ended December 31, 2006, includes compensation cost for all share-based payments granted prior to, but not yet vested as of January 1, 2006, based on the grant date fair value estimated in accordance with the original provisions of SFAS 123 amortized on a graded vesting basis over the options’ vesting period, and compensation cost for all share-based payments granted subsequent to January 1, 2006, based on the grant-date fair value estimated in accordance with the provisions of SFAS 123R amortized on a straight-line basis over the options’ vesting period. We elected to use the modified prospective transition method as permitted by SFAS 123R and, therefore, have not restated our financial results for prior periods to reflect expensing of share-based compensation. As a result, the results for the year ended December 31, 2006, are not comparable to the years ended December 31, 2005 and 2004.

In November of 2005, the FASB issued FASB Staff Position FAS 123(R)-3, “Transition Election Related to Accounting for the Tax Effects of Share Base Payment Awards,” which allowed a one-time election to adopt one of two acceptable methodologies for calculating the initial additional paid-in capital pool (“APIC pool”). We elected the “short-cut” method to establish our APIC pool required under FAS 123(R) for the year ended December 31, 2006. In subsequent periods, the APIC pool will be increased by tax benefits from share-based compensation and decreased by tax deficiencies caused when the recorded share-based compensation for book purposes exceeds the allowable tax deduction.

Prior to the adoption of SFAS 123R, our Board of Directors approved the acceleration of vesting of all outstanding employee share options with an exercise price greater than $3.00 per share. Because the exercise price of all the accelerated options exceeded the market price per share of the common shares as of the new measurement date, the acceleration had no impact on our earnings in 2005. Since the accelerated options had exercise prices in excess of the current market value of our common shares, the options had limited economic value and were not fully achieving their original objective of incentive compensation and employee retention. The modification allows expense recognized after the adoption of SFAS 123R to better reflect our compensation strategies.

During the year ended December 31, 2006, we recognized $1.0 million in share-based compensation expense. At December 31, 2006, there was $1.2 million of unrecognized share-based compensation expense related to unvested shares with a weighted average remaining recognition period of 2.6 years.

Liquidity and Capital Resources

Cash, cash equivalents and short-term investments at December 31, 2006, was $46.4 million compared with $43.5 million at December 31, 2005. This $2.9 million increase reflects cash used in operations of $33.3 million, cash used in the purchase of fixed assets of $8.5 million and cash transferred to restricted cash of $4.3 million more than offset by cash provided by financing activities of $48.9, primarily from our term loan financing of $35.0 million and $12.5 million in New Notes issued for cash in our convertible debt exchange.

Net cash used in operating activities was $33.3 million in 2006 compared with $44.2 million in 2005 and $44.8 million in 2004.

Cash used in operations for 2006, consisted of a net loss of $51.8 million with non-cash addbacks for the revaluation of our embedded derivative of $6.9 million, depreciation and amortization of $6.2 million, equity related compensation of $2.1 million and accrued interest of $1.2 million along with a net increase in liabilities of $10.4 million partially offset by an increase in assets of $8.2 million. During 2006, we made payments of $2.7 million for debt issuance costs on our convertible debt of which $2.0 million related to cash used in operations, $3.8 million for interest on our convertible debt and $1.1 million for our Management Incentive Compensation Program (“MICP”).

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Cash used in operations for 2005, consisted of a net income of $2.8 million with non-cash deductions of $40.9 million for a gain on the extinguishment of our debt with Genentech and a $0.3 million gain on a sale of investments along with a net increase in assets of $4.2 million and a net decrease in liabilities of $10.4 million partially offset by non-cash addbacks for depreciation and amortization of $5.8 million, equity related compensation of $1.4 million and accrued interest of $1.7 million. During 2005, we made payments of $4.0 million on our Genentech collaboration liability, $1.9 million for interest on our convertible debt and $1.3 million for our MICP.

Cash used in operations for 2004, consisted of a net loss of $78.9 million with non-cash addbacks for depreciation and amortization of $4.6 million, equity related compensation of $0.9 million and accrued interest of $0.6 million along with a net decrease in assets of $9.6 million and a net increase in liabilities of $18.3 million. During 2004, we made payments of $7.3 million on our Genentech collaboration liability and $1.0 million for our MICP.

Net cash used in investing activities for 2006, 2005 and 2004 was $8.4 million, $27.4 million and $2.6 million, respectively. Cash used investing activities consisted of purchases of property and equipment of $8.5 million, $4.8 million and $2.6 million and net purchases of short-term investments of $(4.4) million, $22.5 million and $(5,000) for 2006, 2005 and 2004, respectively. In addition, $4.3 million was transferred to restricted cash in 2006.

Net cash provided by (used in) financing activities in 2006, 2005 and 2004 was $48.9 million, $68.6 million and $(13.5) million, respectively. Financing activities in 2006, consisted of $35.0 million from our term loan, offset by $1.5 million in debt issuance costs, $12.5 million in proceeds from the issuance of convertible notes, offset by $0.5 million in debt issuance costs, a $3.0 million advance on our line-of-credit with Novartis and $0.4 million in proceeds from the issuance of common shares. Financing activities in 2005, consisted of an issuance of $60.0 million of convertible senior notes for net proceeds of $56.4 million, a $12.4 million drawdown on our Novartis loan facility and $0.2 million in proceeds from the issuance of common shares partially offset with principal payments on capital lease obligations of $0.2 million and payments of short-term loan obligations of $0.1 million. Financing activities in 2004 consisted of a $13.2 million payment to retire our short-term loan obligation to Genentech, a $5.0 million payment of our convertible debt to Millennium, $0.6 million for principal payments on capital lease obligations and $0.4 million for principal payments on a short-term loan partially offset by $3.7 million in proceeds from common shares sold under our investment agreement with Millennium, $1.4 million in proceeds from the sale of common shares through share option exercises and the employee share purchase plan and $0.5 million in proceeds from a short-term note.

On November 9, 2006, XOMA (US) LLC entered into a five-year, $35.0 million term loan facility (“the facility”) with Goldman Sachs and borrowed the full amount thereunder. The loan is guaranteed by XOMA. Indebtedness under the facility will bear interest at an annual rate equal to six-month LIBOR plus 5.25%, which was 10.637% at December 31, 2006, and is secured by all rights to receive payments due XOMA (US) LLC relating to RAPTIVA^®, LUCENTIS^® and CIMZIA^™ and other assets. Payments received by XOMA (US) LLC in respect of these payment rights, in addition to a standing reserve of the next semi-annual interest payment, will be held in a custodial account which is classified as restricted cash. This cash account and the interest earned thereon can be used solely for the payment of the interest amounts in March and September of each year and, at that time, amounts in excess of the interest reserve requirement may be used to pay down principal or be distributed back to us, at the discretion of the lender. XOMA (US) LLC may prepay indebtedness under the facility at any time, subject to certain prepayment premiums. XOMA (US) LLC is required to comply with a debt covenant determined by the ratio of royalties collected to interest payable. Proceeds from the loan will be used for general corporate purposes.

At December 31, 2006, the outstanding principal amount under this loan totaled $35.0 million and the balance in restricted cash was $4.3 million. Debt issuance costs of $1.5 are being amortized on a straight-line basis over the five year life of the loan and are disclosed as current and long-term debt issuance costs on the balance sheet. In 2006, we incurred interest expense payable of $0.5 million and amortization of debt issuance costs of $42,000.

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In February of 2005, we issued $60.0 million of 6.5% convertible senior notes due in 2012, the proceeds of which are being used for general corporate purposes, including current research and development projects, the development of new products or technologies, equipment acquisitions, general working capital purposes and operating expenses. The notes were initially convertible into approximately 32 million common shares at a conversion rate of 533.4756 of our common shares per $1,000 principal amount of notes, which is equivalent to a conversion price of approximately $1.87 per common share. The convertible senior notes were issued, to the initial purchasers, for net proceeds of $56.6 million. The issuance costs of approximately $3.4 million are being amortized on a straight-line basis over the 84 month life of the notes, and are disclosed as current and long-term debt issuance costs on the balance sheet.

In February of 2006, we completed an exchange offer with holders of our 6.5% convertible senior notes due 2012 in which we exchanged $60.0 million aggregate principal amount of our new 6.5% Convertible SNAPs_SM due 2012 (the “New Notes”) for all $60.0 million aggregate principal amount of our then outstanding convertible senior notes due 2012. We also issued an additional $12.0 million of New Notes to the public for cash at a public offering price of 104% of principal, or $12.5 million. The New Notes are initially convertible into approximately 38.4 million common shares at a conversion rate of 533.4756 of common shares per $1,000 principal amount of New Notes, which is equivalent to a conversion price of approximately $1.87 per common share. Before February 10, 2010, we may not redeem the New Notes. On or after February 10, 2010, we may redeem any or all of the New Notes at 100% of the principal amount, plus accrued and unpaid interest. In addition, we may automatically convert some or all of the New Notes on or prior to the maturity date if the closing price of our common shares has exceeded 150% of the conversion price then in effect for at least 20 trading days during any consecutive 30 trading day period ending within five trading days prior to the notice of auto-conversion. If we elect to automatically convert, or if holders elect to voluntarily convert, some or all of the New Notes on or prior to February 10, 2010, we must pay or provide for additional interest equal to four years’ worth of interest less any interest paid or provided for, on the principal amount so converted, prior to the date of conversion. Additional interest, if any, shall be paid in cash or, solely at our option and subject to certain limitations, in our common shares valued at the conversion price then in effect.

In accounting for the New Notes, we applied guidance as set forth in EITF 96-19, Statement of Financial Accounting Standards No. 133, “Accounting for Derivative Instruments and Hedging Activities,” as amended (“SFAS 133”), EITF 05-7, EITF 00-19, and EITF 01-6 as follows. The exchange offer is a modification of existing debt, rather than an extinguishment. The additional interest payment upon conversion is an embedded derivative requiring separate accounting. We considered the provisions of EITF 05-2 and concluded that this is not conventional convertible debt.

In accordance with SFAS 133, we have separately accounted for the additional interest payment feature of the New Notes as an embedded derivative instrument, which is measured at fair value and classified on the balance sheet with the convertible debt. Changes in the fair value of the embedded derivative are recognized in earnings as a component of other income (expense). At the time of issuance, we estimated the fair value of the additional interest payment feature to be $5.8 million, including approximately $1.0 million related to the New Notes issued for cash, based on current information including share price. For the New Notes issued in the exchange offer and in the new money offering, this amount was subtracted from the carrying value of the debt, reflected as a debt discount, which is amortized as interest expense using the effective interest method through the date the notes are scheduled to mature, and separately reported as a derivative liability.

The additional New Notes were issued, to the initial purchasers, for net proceeds of $11.8 million. Debt issuance costs related to the New Notes of approximately $0.7 million are being amortized on a straight-line basis over the 72 month life of the notes. Additional debt issuance costs of $2.0 million, related to the modification of the existing debt, were expensed as incurred with $1.1 million and $0.9 million expensed during 2006 and 2005, respectively.

For the year ended December 31, 2006, $27.5 million of New Notes were converted into 18,262,264 common shares including 3,602,879 shares related to the additional interest payment feature of the notes. As of

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December 31, 2006, we have elected to pay all additional interest owed in common shares. We recorded a $6.9 million charge to interest expense during the year ended December 31, 2006, as a result of an increase in the fair value of the embedded derivative on our convertible debt including $4.8 million related to the additional interest feature of the converted notes. The remaining principal of $44.5 million is convertible into 23,750,873 common shares and 1,889,317 common shares remain available for payment of the additional interest feature.

For the years ended December 31, 2006 and 2005, we incurred $3.4 million and $3.5 million, respectively, in interest expense payable on our convertible debt. Interest expense is payable on a semi-annual basis. Additionally, we amortized a net of $1.0 million in debt issuance costs, premium and discount for the year ended December 31, 2006, and $0.5 million in debt issuance costs for the year ended December 31, 2005. See “Subsequent Events” at the end of this section for an update on our convertible debt.

In May of 2005, we executed a secured note agreement with Novartis. Under the note agreement, Novartis agreed to make semi-annual loans to us, to fund up to 75% of our research and development and commercialization costs under the collaboration arrangement, not to exceed $50.0 million in an aggregate principal amount. Any unpaid principal amount together with accrued and unpaid interest shall be due and payable in full on June 21, 2015, the tenth anniversary date of the advance date on which the first loan was made. Interest on the unpaid balance of the principal amount of each loan shall accrue at a floating rate per annum which was equal to 7.37% at December 31, 2006, and is payable semi-annually in June and December of each year. At our election, the semi-annual interest payments can be added to the outstanding principal amount, in lieu of a cash payment, as long as the aggregate principal amount does not exceed $50.0 million. Loans under the note agreement are secured by our interest in the collaboration with Novartis, including our share of any profits arising therefrom. At December 31, 2006, the outstanding principal balance under this note agreement totaled $16.4 million and for the years ended December 31, 2006, and 2005, we incurred and capitalized interest expense of $1.0 million and $0.3 million, respectively.

Payments by period due under contractual obligations at December 31, 2006, mature as follows (in thousands):

In addition to the above, we have committed to make potential future “milestone” payments to third parties as part of licensing and development programs. Payments under these agreements generally become due and payable only upon the achievement of certain developmental, regulatory and/or commercial milestones. Because it is uncertain if and when these milestones will be achieved, such contingencies have not been recorded on our consolidated balance sheet.

Other than the convertible senior notes, the term loan, the Novartis note and the operating lease obligations stated in the table above, we had no other long-term obligations as of December 31, 2006, nor any purchase obligations, as defined in Item 303(a)(5) of Regulation S-K since all of our outstanding purchase obligations are cancelable.

The present outlook is for lower losses in 2007 as compared with 2006. Our strategy is to attempt to continue broadening our product pipeline through internal development, additional collaborations such as our

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arrangements with Lexicon, Novartis, SPRI and Takeda and additional government and other external contracts such as those with NIAID, AVEO and Taligen; and to increase revenues or benefits from cost sharing arrangements which take advantage of our manufacturing and development capabilities.

We expect our cash, cash equivalents and short-term investments to decrease during 2007 as a result of the use of cash to fund ongoing operations and capital investments. Additional licensing and antibody discovery collaboration agreements may positively impact our cash balances.

Based on current spending levels, anticipated revenues, collaborator funding, proceeds from our convertible note offerings in February of 2005 and February of 2006, our November 2006 term loan and other sources of funding we believe to be available, we estimate that we have sufficient cash resources to meet our anticipated net cash needs through at least 2008. Any significant revenue shortfalls, increases in planned spending on development programs or more rapid progress of development programs than anticipated, as well as the unavailability of anticipated sources of funding, could shorten this period. Progress or setbacks by potentially competing products may also affect our ability to raise new funding on acceptable terms. For a further discussion of the risks related to our business and their effects on our cash flow and ability to raise new funding on acceptable terms, see “Risk Factors” included in Item 1A.

Although operations are influenced by general economic conditions, we do not believe that inflation had a material impact on financial results for the periods presented. We believe that we are not dependent on materials or other resources that would be significantly impacted by inflation or changing economic conditions in the foreseeable future.

Recent Accounting Pronouncements

In July of 2006, the Financial Accounting Standards Board (“FASB”) issued FASB Interpretation No. 48, “Accounting for Uncertainty in Income Taxes” (“FIN 48”), an interpretation of FASB Statement No. 109, “Accounting for Income Taxes” (“FAS 109”). FIN 48 clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statements in accordance with FAS 109 and prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. FIN 48 also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure and transition. FIN 48 will be effective beginning with the first annual period after December 15, 2006. We are still evaluating what impact, if any, the adoption of this standard will have on our financial position or results of operations.

In September of 2006, the FASB issued Statement of Financial Accounting Standards No. 157, “Fair Value Measurements” (“SFAS 157”). SFAS 157 provides guidance for using fair value to measure assets and liabilities and responds to investors’ request for expanded information about the extent to which companies measure assets and liabilities at fair value, the information used to measure fair value and the effect of fair value measurements on earnings. SFAS 157 applies whenever other standards require or permit assets or liabilities to be measured at fair value and does not expand the use of fair value in any new circumstances. SFAS will be effective beginning with the first annual period after November 15, 2007. We are still evaluating what impact, if any, the adoption of this standard will have on our financial position or results of operations.

Subsequent Events

On February 26, 2007, Jack Castello, Chairman of the Board, President and Chief Executive Officer of XOMA, announced his plans to retire. Mr. Castello will continue to serve in his present capacities during the candidate search and transition period.

On February 28, 2007, we announced that pursuant to the terms of our collaboration agreement with Novartis, the parties’ mutual obligations to conduct antibody discovery, development and commercialization

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work together on an exclusive basis in oncology have expired, except with respect to existing collaboration projects which have reached the development stage. Unamortized deferred revenue of $4.3 million, at December 31, 2006, associated with the upfront collaboration fee of $10.0 million will be recognized during the first quarter of 2007. Prior to the expiration of the exclusivity period, the upfront fee was being amortized over the expected five-year term of the exclusivity provision, or at a rate of $0.5 million a quarter. All other terms of the collaboration remain in effect.

On February 28, 2007, in conjunction with Takeda, we announced that we had amended our existing collaboration agreement to increase the number of potential therapeutic antibody programs in oncology under our collaboration initiated in November of 2006.

As of March 7, 2007, an additional $42.0 million of our New Notes were converted into 24,223,414 common shares, including 1,790,759 shares related to the additional interest payment feature of the notes. As a result of the limitation on shares available to satisfy the additional interest feature, we also paid $4.9 million of additional interest in cash. At the time of the note conversions, we recorded a $5.8 million charge to interest expense as a result of the revaluation to fair value of the embedded derivative related to the additional interest feature of the notes. The remaining outstanding principal amount of the notes of $2.5 million is convertible into 1,416,776 common shares with 98,558 shares available to pay the additional interest feature.

On March 7, 2006, we announced that the conditions necessary for the auto-conversion of the remaining $2.5 million principal outstanding of our convertible debt had been met and that we had elected to notify note holders of our intention to redeem any notes not converted and still outstanding as of March 27, 2007.

Forward-Looking Information And Cautionary Factors That May Affect Future Results

Certain statements contained herein related to the sufficiency of our cash resources, levels of future revenues, losses, expenses and cash, future sales of approved products, as well as other statements related to current plans for product development and existing and potential collaborative and licensing relationships, or that otherwise relate to future periods, are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements are based on assumptions that may not prove accurate. Actual results could differ materially from those anticipated due to certain risks inherent in the biotechnology industry and for companies engaged in the development of new products in a regulated market. Among other things, the period for which our cash resources are sufficient could be shortened if expenditures are made earlier or in larger amounts than anticipated or are unanticipated, if anticipated revenues or cost sharing arrangements do not materialize, if funds are not otherwise available on acceptable terms; revenue levels may be other than as expected if sales of approved products are lower than expected; losses may be other than as expected for any of the reasons affecting revenues and expenses; expense levels and cash utilization may be other than as expected due to unanticipated changes in our research and development programs; and the sales efforts for approved products may not be successful if the parties responsible for marketing and sales fail to meet their commercialization goals, due to the strength of the competition, if physicians do not adopt the product as treatment for their patients or if remaining regulatory approvals are not obtained. These and other risks, including those related to the results of pre-clinical testing; the timing or results of pending and future clinical trials (including the design and progress of clinical trials; safety and efficacy of the products being tested; action, inaction or delay by the FDA, European or other regulators or their advisory bodies; and analysis or interpretation by, or submission to, these entities or others of scientific data); changes in the status of existing collaborative relationships; the ability of collaborators and other partners to meet their obligations; our ability to meet the demand of the United States government agency with which we have entered our first government contract; competition; market demands for products; scale-up and marketing capabilities; availability of additional licensing or collaboration opportunities; international operations; share price volatility; our financing needs and opportunities; uncertainties regarding the status of biotechnology patents; uncertainties as to the costs of protecting intellectual property; and risks associated with our status as a Bermuda company, are described in more detail in “Item 1A—Risk Factors”.

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Interest Rate Risk

Our exposure to market rate risk for changes in interest rates relates primarily to our investment portfolio and our loan facility. By policy, we make our investments in high quality debt securities, limit the amount of credit exposure to any one issuer, limit duration by restricting the term of the instrument and hold investments to maturity except under rare circumstances. We do not invest in derivative financial instruments.

In November of 2006, we entered into a five-year senior term loan facility in the aggregate amount of $35.0 million with the principal due at maturity. Interest on the facility will be at a rate of USD six month LIBOR plus 5.25%, which was 10.637% at December 31, 2006.

In February of 2005, we issued $60.0 million of 6.5% convertible senior notes due 2012. In February of 2006, we completed an exchange offer for all $60.0 million of our 6.5% convertible senior notes due 2012 for $60.0 million of 6.5% convertible SNAPs_SM due 2012 (the “New Notes”) and issued an additional $12.0 million of New Notes to the public for cash. The interest rate and amount of principal of the previously outstanding notes were, and of the New Notes are, fixed. The New Notes include an additional interest rate feature which is accounted for as an embedded derivative which is measured at fair value. Changes in the fair value of the embedded derivative are recognized in earnings as interest expense.

As of December 31, 2006, we have drawn down $16.4 million against the Novartis $50.0 million loan facility that is due in 2015 at an interest rate of USD six month LIBOR plus 2 percent which was 7.37% at December 31, 2006.

We estimate that a hypothetical 100 basis point change in interest rates could increase or decrease our interest expense by approximately $521,000 on an annualized basis.

We hold interest-bearing instruments that are classified as cash, cash equivalents and short-term investments. Fluctuations in interest rates can affect the principal values and yields of fixed income investments. If interest rates in the general economy were to rise rapidly in a short period of time, our fixed income investments could lose value. The following table presents the amounts and related weighted interest rates of our cash and investments at December 31, 2006 and 2005, (in thousands, except interest rate):

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The following consolidated financial statements of the registrant, related notes and report of independent registered public accounting firm are set forth beginning on page F-1 of this report.