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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

For the quarterly period ended March 31, 2005

Commission File No. 0-14710

XOMA Ltd.

(Exact name of registrant as specified in its charter)

2910 Seventh Street, Berkeley, CA 94710

(Address of principal executive offices, including zip code)

(510) 204-7200

(Registrant’s telephone number, including area code)

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 whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Securities Exchange Act of 1934).    Yes  x    No  ¨

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date.

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XOMA Ltd.

FORM 10-Q

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PART I - FINANCIAL INFORMATION

XOMA Ltd.

CONDENSED CONSOLIDATED BALANCE SHEETS

(in thousands)

See accompanying notes to condensed consolidated financial statements.

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X OMA Ltd.

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(unaudited, in thousands, except per share amounts)

See accompanying notes to condensed consolidated financial statements.

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XOMA Ltd.

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS

(unaudited, in thousands)

See accompanying notes to condensed consolidated financial statements.

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XOMA Ltd.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(unaudited)

Business

XOMA Ltd. (“XOMA” or the “Company”), a Bermuda company, is a biopharmaceutical company that develops for commercialization antibodies and other genetically-engineered protein products to treat immunological and inflammatory disorders, cancer and infectious diseases. The Company’s products are presently in various stages of development and most are subject to regulatory approval before they can be introduced commercially. The Company has an interest in one approved product, RAPTIVA^®, which is marketed in the United States, Europe and elsewhere, for the treatment of moderate-to-severe plaque psoriasis under a royalty agreement with Genentech, Inc. (“Genentech”). XOMA’s pipeline includes both proprietary products and collaborative programs at various stages of preclinical and clinical development.

Basis of Presentation

The condensed consolidated financial statements include the accounts of XOMA and its subsidiaries. All significant intercompany accounts and transactions were eliminated during consolidation. The unaudited financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q. These financial statements and related disclosures have been prepared with the assumption that users of the interim financial information have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these statements should be read in conjunction with the audited Consolidated Financial Statements and related Notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2004, filed with the SEC on March 15, 2005.

In the opinion of management, the unaudited condensed consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, which are necessary to present fairly the Company’s consolidated financial position as of March 31, 2005, the consolidated results of the Company’s operations for the three months ended March 31, 2005 and 2004, and the Company’s cash flows for the three months then ended. The condensed consolidated balance sheet amounts at December 31, 2004, have been derived from audited consolidated financial statements. The interim results of operations are not necessarily indicative of the results that may occur for the full fiscal year or future periods.

Critical Accounting Policies

The Company believes that there have been no significant changes in its critical accounting policies during the three months ended March 31, 2005, as compared with those previously disclosed in its Annual Report on Form 10-K for the year ended December 31, 2004, filed with the SEC on March 15, 2005.

Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities, if any, at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from those estimates.

Concentration of Risk

Cash, cash equivalents, short-term investments and accounts receivable are financial instruments, which potentially subject the Company to concentrations of credit risk. The Company maintains money market funds and short-term investments that bear minimal risk. The Company has not experienced any significant credit losses and does not generally require collateral on receivables. For the three months ended March 31, 2005, three customers represented 66%, 17% and 15% of total revenues and, as of March 31, 2005, one of these customers had outstanding receivables of $0.5 million. For the three months ended March 31, 2004, three customers represented 59%, 18% and 15% of total revenues and, as of March 31, 2004, there were no billed or unbilled receivables outstanding from these customers.

Share-Based Compensation

In accordance with the provisions of the Statement of 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 – an amendment of SFAS No. 123,” the Company has elected to continue to follow Accounting Principles Board Opinion No. 25, “Accounting for Stock Issued to Employees” (“APB 25”) and related interpretations and to adopt the

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XOMA Ltd.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(unaudited)

“disclosure only” alternative described in SFAS 123. Under APB 25, if the exercise price of the Company’s employee share options equals or exceeds the fair market value on the date of the grant or the fair value of the underlying shares on the date of the grant as determined by the Company’s Board of Directors, no compensation expense is recognized. Accordingly, the financial statements reflect amortization of compensation resulting from options granted at exercise prices which were below market price at the grant date. Had compensation cost for the Company’s share-based compensation plans been based on the fair value method at the grant dates for awards under these plans consistent with the provisions of SFAS 123, the Company’s net income (loss) and net income (loss) per share would have been decreased (increased) to the pro forma amounts indicated below for the three months ended March 31, 2005 and 2004 (in thousands, except per share amounts):

The fair value of each option grant under these plans is estimated on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions used for grants during the periods indicated below:

Comprehensive Income (Loss)

Unrealized gains or losses on the Company’s available-for-sale securities are included in other comprehensive income (loss). Comprehensive income (loss) and its components for the three months ended March 31, 2005 and 2004, are as follows (in thousands):

Net Income (Loss) Per Common Share

Basic net income (loss) per common share is based on the weighted average number of common shares outstanding during the period. Diluted net income (loss) per common share is based on the weighted average number of common shares and other dilutive securities outstanding during the period, provided that including these dilutive securities does not increase (decrease) the net income (loss) per share.

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XOMA Ltd.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(unaudited)

The following dilutive outstanding securities were considered in the computation of diluted net income per share. Those that are antidilutive were not included in the computation of diluted net income (loss) per share (in thousands):

The following is a reconciliation of the numerators and denominators of the basic and diluted net income (loss) per share (in thousands):

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):

Recent Accounting Pronouncements

In December of 2004, the FASB issued SFAS No. 123 (revised 2004), “Share-Based Payment”, which replaces SFAS No. 123, “Accounting for Stock-Based Compensation,” and supercedes APB Opinion No. 25, “Accounting for Stock Issued to Employees.” SFAS 123R requires all share-based payments to employees, including grants of employee stock options, to be recognized in the financial statements based on their fair values beginning with the first annual period after June 15, 2005, with early adoption encouraged. The pro forma disclosures previously permitted under SFAS 123 no longer will be an alternative to financial statement recognition. XOMA is required to adopt SFAS 123R in the year beginning January 1, 2006. Under SFAS 123R, the Company must determine the appropriate fair value model to be used for valuing share-based payments, the amortization method for compensation cost and the transition method to be used at date of adoption. The transition methods include prospective and retroactive adoption options. Under the retroactive option, prior periods may be restated either as of the beginning of the year of adoption or for all periods presented. The prospective method requires that compensation expense be recorded for all unvested stock options and restricted stock at the beginning of the first quarter of adoption of SFAS 123R, while the retroactive method would record compensation expense for all unvested stock options and restricted stock beginning with the first period restated.

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XOMA Ltd.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(unaudited)

The Company is evaluating the requirements of SFAS 123R and expects that the adoption of SFAS 123R may have a material impact on its consolidated results of operations and earnings per share. The Company has not yet determined the method of adoption or the effect of adopting SFAS 123R, and has not determined whether the adoption will result in amounts that are similar to the current pro forma disclosures under SFAS 123.

The Company’s Board of Directors approved the acceleration of the vesting of all outstanding employee share options with an exercise price greater than $3.00 per share, effective April 15, 2005.

In January of 2005, the Company announced a restructuring of its arrangement with Genentech on RAPTIVA^®. Under the restructured arrangement, effective January 1, 2005, XOMA will be entitled to receive mid-single digit royalties on worldwide sales of RAPTIVA^®. 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 XOMA may agree to provide further clinical trial or other development services at Genentech’s expense. In addition, XOMA’s obligation to pay its outstanding balance to Genentech of $40.9 million under a development loan was extinguished. In 2004, XOMA recorded collaboration arrangement expense of $16.4 million, incurred an additional $3.9 million of RAPTIVA^® costs included in its research and development expenses, and recorded $1.0 million in interest expense related to the development loan. In the first quarter of 2005, the Company recorded a one-time credit to other income of $40.9 million related to the extinguishment of the loan obligation.

In March of 2005, the Company was awarded a $15.0 million contract from the National Institute of Allergy and Infectious Diseases (“NIAID”), a part of the National Institutes of Health (NIH), to develop three anti-botulinum neurotoxin monoclonal antibody therapeutics. The contract work will be performed over an eighteen month period and will be 100% funded with Federal funds from NIAID under Contract No. HHSN266200500004C. The Company is recognizing revenue over the life of the contract as the services are performed and, as per the terms of the contract, a 10% retention on all revenue is being deferred until completion of the contract.

In February of 2005, XOMA issued $60.0 million of 6.5% convertible senior notes due February 1, 2012. The notes are initially convertible into approximately 32 million common shares at a conversion rate of 533.4756 of XOMA 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, the Company may not redeem the notes. On or after February 6, 2008, the Company may redeem any or all of the notes at 100% of the principal amount, plus accrued and unpaid interest, if its common shares trade at 150% of the conversion price then in effect for 20 trading days in a 30 consecutive trading day period. Holders of the notes may require XOMA 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 as defined in the indenture governing the notes. In addition, following certain fundamental changes, the Company will increase the conversion rate up to 50 common shares per $1,000 principal amount of notes which would increase the number of shares into which the notes are convertible by up to 3 million common shares or, in lieu thereof, it may, in certain circumstances, elect to adjust the conversion rate and related conversion obligation so that the notes are convertible into shares of the acquiring, continuing or surviving company.

The 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.

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XOMA Ltd.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(unaudited)

During the quarter ended March 31, 2005, the Company restructured its clinical organization to a level needed to support its current clinical activity. As a result of the restructuring, the Company recorded charges of $461,000 for severance and related benefits of which $330,000 remained outstanding at March 31, 2005. These charges are included in research and development expenses.

In November of 2004, a complaint was filed in the United States District Court, Northern District of California, in a lawsuit captioned Physicians Executive Business Corp. v. XOMA Ltd., et al., No. C 04 4878, by an investor in XOMA’s common shares. The complaint asserts claims for alleged fraud and negligent misrepresentation relating to events preceding the announcement of Phase II trial results for XMP.629 in August of 2004. The complaint seeks unspecified compensatory damages. XOMA filed a motion to dismiss the complaint and that motion was granted with leave to amend on April 27, 2005. Plaintiff has until May 20, 2005, to file an amended complaint. The Company intends to continue to vigorously defend against this lawsuit.

In April of 2005, a complaint was filed in the Circuit Court of Cook County, Illinois, in a lawsuit captioned Hanna v. Genentech, Inc. and XOMA (US) LLC, No. 2005L00438B, by an alleged participant in one of the clinical trials of RAPTIVA^®. The complaint asserts claims for alleged strict product liability and negligence against Genentech and XOMA based on injuries alleged to have occurred as a result of plaintiff’s treatment in the clinical trial. The complaint seeks unspecified compensatory damages alleged to be in excess of $100,000. Given that this lawsuit was filed only recently, the Company has not yet fully assessed its merits; however, it intends to vigorously investigate and pursue available defenses.

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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, stock 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.

Results of Operations

Revenues

Revenues for the three months ended March 31, 2005, were $3.0 million compared with $0.2 million for the three months ended March 31, 2004.

License and collaborative fees revenues were $0.5 million for the three months ended March 31, 2005, compared with $0.2 million for the three months ended March 31, 2004. These revenues include upfront and milestone payments related to the outlicensing of our products and technologies and other collaborative arrangements. The increase of $0.3 million resulted primarily from amortization of the $10.0 million in upfront payments received from our oncology collaboration with Chiron Corporation (“Chiron”), which is being recognized as revenue over the five year expected term of the agreement. The amortization of this payment began in the second quarter of 2004.

Contract revenues were $1.3 million for the three months ended March 31, 2005, compared with zero for the three months ended March 31, 2004. The increase resulted primarily from clinical trial services performed on behalf of Genentech, Inc. (“Genentech”) and contract manufacturing services performed under the National Institute of Allergy and Infectious Diseases (“NIAID”) contract entered into in March of 2005, to develop three anti-botulinum neurotoxin monoclonal antibody therapeutics. The contract work will be performed over an eighteen month period and will be 100% funded with Federal funds from NIAID under Contract No. HHSN266200500004C. We are recognizing revenue over the life of the contract as the services are performed and, as per the terms of the contract, a 10% retention on all revenue is being deferred until completion of the contract.

Royalties were $1.2 million for the three months ended March 31, 2005, compared with zero for the three months ended March 31, 2004. The increase resulted primarily from RAPTIVA^® royalties earned under our restructured arrangement with Genentech. Beginning on January 1, 2005, we are earning a mid-single digit royalty on worldwide sales of RAPTIVA^®.

Research and development expenses consist of direct and research-related allocated overhead costs such as salaries and related personnel costs, facilities costs, patent costs and material and supply costs in addition to costs related to clinical trials to validate our testing processes and procedures and related overhead expenses. Research and development expenses consist of independent research and development and costs associated with collaborative research and development arrangements as well as contract research and development arrangements. Research and development expenses for the three months ended March 31, 2005, were $10.0 million compared with $13.0 million for the same period of 2004, a decrease of 23%. This decrease reflected increased spending on our Chiron oncology collaboration and our anti-gastrin antibody collaboration with Aphton Corporation (“Aphton”), which was more than offset by decreases in spending on MLN2222, XMP.629, RAPTIVA^®, TPO mimetic and new product research. Additionally, during the quarter ended March 31, 2005, research and development expenses included $0.5 million in costs for severance and benefits related to the restructuring of our clinical organization. This area was restructured to a level needed to support our current clinical activity.

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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 be divided into those related to our internal projects and external projects related to collaborative arrangements and research and development service contracts. The costs related to internal projects versus external projects approximate the following (in thousands):

For the three months ended March 31, 2005, one development program (Chiron) accounted for more than 20% but less than 30% and no development program accounted for more than 30% of our total research and development expenses. For the three months ended March 31, 2004, three development programs (MLN2222, XMP.629 and RAPTIVA^®) 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.

General and administrative expenses include salaries and related personnel costs, facilities costs and professional fees. General and administrative expenses for the three months ended March 31, 2005, were $3.8 million compared with $3.9 million for the three months ended March 31, 2004.

Collaborative arrangement expenses, which related exclusively to RAPTIVA^® were zero and $3.2 million for the three months ended March 31, 2005 and 2004, respectively. The 2004 amount reflects our 25% share of commercialization costs for RAPTIVA^® in excess of Genentech’s revenues less cost of goods sold and research and development cost sharing adjustments. 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 R&D expenses, but rather we are entitled to receive royalties on worldwide sales. Genentech will be 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.

Investment and interest income for the three months ended March 31, 2005, was $0.6 million compared with $0.2 million for the same period of 2004. The $0.4 million increase resulted primarily from the gain on the sale of our remaining short-term investments and increased interest rates.

Interest expense for the three months ended March 31, 2005, was $0.7 million compared with $0.3 million for the same period of 2004. The $0.4 million increase in 2005 compared with 2004 resulted primarily from the interest incurred on our $60.0 million in convertible notes issued in February of 2005 partially offset by a reduction in interest as a result of the repayment of our Genentech and Millennium Pharmaceuticals, Inc. (“Millennium”) convertible notes which were outstanding in 2004.

Other income for the three months ended March 31, 2005, was $40.9 million compared with zero for the three months ended March 31, 2004. The 2005 amount reflects the one-time credit related to the extinguishment of the Genentech development loan that was outstanding at December 31, 2004, as a result of the restructuring of the Genentech agreement, which was announced in January of 2005.

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Liquidity and Capital Resources

Cash, cash equivalents and short-term investments at March 31, 2005, was $61.7 million compared with $24.3 million at December 31, 2004. This $37.4 million increase primarily reflects cash from our February financing of $56.6 million partially offset by cash used in operation of $18.8 million.

Net cash used in operating activities was $18.8 million for the three months ended March 31, 2005, compared with $2.8 million for the three months ended March 31, 2004. Net cash used in operating activities for the three months ended March 31, 2005, resulted primarily from a net income of $30.1 million, depreciation and amortization of $1.1 million, common shares issued under employee 401(k) and management incentive plans of $1.3 million and accrued interest on convertible notes of $0.6 million more than offset by the gain on extinguishment of long-term debt of $40.9 million, the gain on sale of investments of $0.3 million and a net decrease in assets and liabilities of $10.7 million. Net cash used in operating activities for the three months ended March 31, 2004, resulted primarily from a net loss of $20.2 million partially offset by depreciation and amortization of $1.1 million, common shares issued under employee 401(k) and management incentive plans of $0.9 million, accrued interest on convertible notes of $0.3 million and a net increase in assets and liabilities of $15.1 million.

Net cash provided by investing activities for the three months ended March 31, 2005, was $0.2 million compared with cash used in investing activities of $0.7 million for the three months ended March 31, 2004. The $0.9 million increase in 2005 compared with 2004 reflected $0.5 million in proceeds from the sale of our short-term securities and a $0.4 million decrease in purchases of property and equipment.

Net cash provided by financing activities was $56.5 million for the three months ended March 31, 2005, compared with cash used in financing activities of $2.8 million for the three months ended March 31, 2004. Financing activities for the first three months of 2005 consisted of an issuance of convertible senior notes for net proceeds of $56.6 million and $0.1 million in proceeds from the issuance of common shares partially offset with capital lease payments of $0.1 million and payments of short-term loan obligations of $0.1 million. Financing activities for the first three months of 2004 consisted of a $3.0 million payment on our short-term loan obligation and $0.2 million in capital lease payments partially offset by $0.4 million in proceeds from the issuance of common shares.

In February of 2005, we issued $60.0 million of 6.5% convertible senior notes due February 1, 2012. The notes are initially convertible into approximately 32 million common shares at a conversion rate of 533.4756 of XOMA 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 may not redeem the notes. On or after February 6, 2008, we may redeem any or all of the notes at 100% of the principal amount, plus accrued and unpaid interest, if our common shares trade at 150% of the conversion price then in effect for 20 trading days in a 30 consecutive trading day period. Holders of the notes may require 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 as defined in the indenture governing the notes. In addition, following certain fundamental changes, we will increase the conversion rate up to 50 common shares per $1,000 principal amount of notes which would increase the number of shares into which the notes are convertible by up to 3 million common shares or, in lieu thereof, it may, in certain circumstances, elect to adjust the conversion rate and related conversion obligation so that the notes are convertible into shares of the acquiring, continuing or surviving company.

The 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.

Our cash, cash equivalents and short-term investments are expected to decrease through 2005 with the use of cash to fund ongoing operations.

Based on current spending levels, anticipated revenues, partner funding, remaining net proceeds received from our last underwritten public offering, and proceeds from our convertible senior notes issued in February of 2005, we estimate that we have sufficient cash resources to meet our anticipated net cash needs through at least 2008. Any significant revenue shortfalls or increases in planned spending on development programs or more rapid progress of development programs could shorten this period. Additional licensing arrangements or collaborations or otherwise entering into new equity or other financing arrangements could extend this period. Progress or setbacks by potentially competing products may also affect our ability to raise new funding on acceptable terms.

Critical Accounting Policies

Critical accounting policies are those that require significant judgment and/or estimates by management at the time that the financial statements are prepared such that materially different results might have been reported if other assumptions had been made. We consider certain accounting policies related to revenue recognition and recognition of research and development expenses to be critical policies. We believe there have been no significant changes to our critical accounting policies since we filed our 2004 Annual

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Report on Form 10-K with the Securities and Exchange Commission on March 15, 2005. For a description of our critical accounting policies, please refer to our 2004 Annual Report on Form 10-K.

Recent Accounting Pronouncements

In December of 2004, the Financial Accounting Standards Board issued SFAS No. 123 (revised 2004), “Share-Based Payment” (“SFAS 123R”), which replaces SFAS No. 123, “Accounting for Stock-Based Compensation,” (“SFAS 123”) and supercedes APB Opinion No. 25, “Accounting for Stock Issued to Employees.” SFAS 123R requires all share-based payments to employees, including grants of employee stock options, to be recognized in the financial statements based on their fair values beginning with the first annual period after June 15, 2005, with early adoption encouraged. The pro forma disclosures previously permitted under SFAS 123 no longer will be an alternative to financial statement recognition. We are required to adopt SFAS 123R beginning January 1, 2005. Under SFAS 123R, we must determine the appropriate fair value model to be used for valuing share-based payments, the amortization method for compensation cost and the transition method to be used at date of adoption. The transition methods include prospective and retroactive adoption options. Under the retroactive option, prior periods may be restated either as of the beginning of the year of adoption or for all periods presented. The prospective method requires that compensation expense be recorded for all unvested stock options and restricted stock at the beginning of the first quarter of adoption of SFAS 123R, while the retroactive method would record compensation expense for all unvested stock options and restricted stock beginning with the first period restated.

We are evaluating the requirements of SFAS 123R and expect that the adoption of SFAS 123R may have a material impact on our consolidated results of operations and earnings per share. We have not yet determined the method of adoption or the effect of adopting SFAS 123R, and have not determined whether the adoption will result in amounts that are similar to the current pro forma disclosures under SFAS 123.

Our Board of Directors approved the acceleration of the vesting of all outstanding employee share options with an exercise price greater than $3.00 per share, effective April 15, 2005.

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

Certain statements contained herein related to our potential for profitability, future sales of RAPTIVA^®, the sufficiency of our cash resources, 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, our ability to achieve profitability will depend on the success of the sales efforts for RAPTIVA^®, revenues related to development services we provide, our ability to effectively anticipate and manage our expenditures and the availability of capital market and other financing; the sales efforts for RAPTIVA^® may not be successful if Genentech or its partner, Serono, S.A. (“Serono”), fails to meet its 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; and 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, or if funds are not otherwise available on acceptable terms. 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; competition; market demand 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 the remainder of this section.

The Marketing And Sales Effort In Support Of The Only Product In Which We Have An Interest That Has Received Regulatory Approval May Not Be Successful.

RAPTIVA^®, the only product in which we have an interest that has received regulatory approval, 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, and Genentech has only commenced the full intended scope of this effort in the United States within the past year. 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. We have no role in marketing and sales efforts. Under our current arrangement with Genentech, we are entitled to receive royalties on worldwide sales of RAPTIVA^®. Successful commercialization of this product is subject to a number of risks, including Genentech’s and Serono’s ability to implement their marketing and sales effort and achieve sales, the strength of competition from other products being marketed or developed to treat psoriasis, physicians’ and patients’ acceptance of RAPTIVA^® as a treatment for psoriasis, Genentech’s ability to provide manufacturing capacity to meet demand for the product, and pricing and reimbursement issues. Certain of these risks are discussed in more detail below.

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, partner funding, remaining net proceeds received from our last underwritten public offering, and proceeds from our convertible senior notes issued in February of 2005, we estimate that we have sufficient cash resources to meet our anticipated net cash needs through at least 2008. Any significant revenue shortfalls or increases in planned spending on development programs or more rapid progress of development programs could shorten this period. Additional

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licensing arrangements or collaborations or otherwise entering into new equity or other financing arrangements could extend 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.

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. Only one of our therapeutic products, RAPTIVA^®, has received regulatory approval. The United States government and governments of other countries extensively regulate many aspects of our products, including:

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. The review of therapeutic biologic products has been transferred within the FDA from the Center for Biologics Evaluation and Research to the Center for Drug Evaluation and Research, the body that reviews drug products. Because implementation of this plan may not be complete, we do not know when or how this change will affect us. 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^®, 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.

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:

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For example,

Given that regulatory review is an interactive and continuous process, we maintain 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.

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 March 31, 2005, we had an accumulated deficit of $648.4 million.

For the three months ended March 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 a net income of approximately $30.1 million or $0.35 per common share (basic) and $0.28 per common share (diluted). For the year ended December 31, 2004, we had a net loss of approximately $78.9 million, or $0.93 per common share (basic and diluted). We expect to incur additional losses in the future.

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 all of 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.

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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.

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 our products, we may not be able to do so on our own. We do not know whether Genentech, Millennium, Chiron, Aphton, Triton or Zephyr 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 Chiron provides for funding by it in the form of periodic loans, and we cannot be certain that Chiron will have the necessary funds available when these loans are to be made. Furthermore, our contract with NIAID contains 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 that this contract is our first with NIAID or any other governmental agency, we are uncertain as to the extent of NIAID’s demands and the flexibility that will be granted to us in meeting those demands.

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.

Primarily as a result of our bacterial cell expression licensing program, we have access to numerous phage display technologies licensed to us by other parties. However, we have had access to these technologies for a relatively short time and, to varying degrees, 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. We cannot be certain that these restrictions or the rights of others will not impede our ability to utilize these technologies.

Because We Have No History Of Profitability And Because The Biotechnology Sector Has Been Characterized By Highly Volatile Stock Prices, Announcements We Make And General Market Conditions For Biotechnology Stocks Could Result In A Sudden Change In The Value Of Our Common Shares.

As a biopharmaceutical company, we have experienced significant volatility in our common shares. 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. From January 1, 2004 through May 3, 2005, our share price has ranged from a high of $7.71 to a low of $0.98. On May 3, 2005, the closing price of the common shares as reported on the Nasdaq National Market was $1.22 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 Be Able To Increase Existing Or Acquire New Manufacturing Capacity Sufficient To Meet Market Demand.

Genentech is responsible for manufacturing or arranging for the manufacturing of commercial quantities of RAPTIVA^®. Should Genentech have difficulty in providing manufacturing capacity to produce RAPTIVA^® in sufficient quantities, we do not know whether they will be able to meet market demand. 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 A Viable Market For RAPTIVA^® Or Our Other Products.

Even though Genentech and we received FDA approval in October of 2003 to market RAPTIVA^® and even if we receive regulatory approval for our other products, our products may not be accepted in the marketplace. 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 RAPTIVA^® if they believe other products to be more effective or are more comfortable prescribing other products. Consequently, we do not know if physicians or patients will adopt or use our products for their approved indications.

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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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^®.

There are at least two competitors developing a complement inhibitor which may compete with MLN2222. Alexion and its partner Proctor & Gamble have initiated enrollment in a second Phase III trial of pexelizumab, a monoclonal antibody. This study is expected to enroll approximately 4,000 patients undergoing coronary artery bypass graft surgery. TP10 is a complement inhibitor developed by AVANT Immunotherapeutics Inc. (“AVANT”) for applications including the limitation of complement-mediated damage following surgery on cardiopulmonary by-pass. AVANT anticipates completing enrollment in the Phase IIb study in 200-300 women undergoing cardiac bypass surgery as soon as possible. AVANT is also working closely with its partner, Lonza Biologics plc, to complete process development and scale-up efforts in preparation for the production of Phase III clinical materials and the start of that trial by year-end 2005.

Currently, there are at least two companies developing topical peptide treatments for acne which may compete with XMP.629. Migenix Inc., formerly Micrologix Biotech, Inc., is developing MBI 594AN, a topical peptide that has completed a Phase IIB trial for the treatment of acne, and Helix Biomedix, Inc. is developing several peptide compounds.

In collaboration with Chiron, we are co-developing the monoclonal antibody 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. SGN-40 is currently in Phase I studies in multiple myeloma and non-Hodgkin’s lymphoma, with an additional Phase I study in chronic lymphocytic leukemia to begin in 2005. Another example is 5d12, an anti-CD40 antibody under development by Tanox, Inc. for Crohn’s disease. Chiron licensed the antibody to Tanox, Inc. in 1995 and retains some commercialization and technology rights.

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.

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If Our And Our Partners’ Patent Protection For Our Principal Products And Processes Is Not Enforceable, We May Not Realize Our Profit Potential.

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 patent position of biotechnology companies generally is highly uncertain and involves complex legal and factual questions, and no consistent policy regarding the breadth of allowed claims has emerged from the actions of the U.S. Patent and Trademark Office with respect to biotechnology patents. Legal considerations surrounding the validity of biotechnology patents continue to be in transition, and historical legal standards surrounding questions of validity may not continue to be applied, and current defenses as to issued biotechnology patents may not in fact be considered substantial in the future. These factors have contributed to uncertainty as to:

The Patent Office has issued approximately 76 patents to us related to our products based on human bactericidal/permeability-increasing protein, which we call BPI, including novel compositions, their manufacture, formulation, assay and use. In addition, we are the exclusive licensee of BPI-related patents and applications owned by NYU and Incyte. These patents and licenses are now licensed and sublicensed to Zephyr. The Patent Office has also issued nine patents to us related to our bacterial expression technology.

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 not be honored 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.

Protecting Our 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, if the litigation included a claim of infringement by us of another party’s patent that was 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.

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 purchases 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 arrangement could result in dilution in the value of our shares.

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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.

The same factors that affect us directly because we are a biotechnology company 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 or 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 bacterial expression 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 may be limited or disrupted by:

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; Patrick J. Scannon, M.D., Ph.D., our Senior Vice President and Chief Scientific and Medical Officer; Peter B. Davis, our Vice President, Finance and Chief Financial Officer; and Christopher J. Margolin, our Vice President, General Counsel and Secretary. We have employment agreements with each of these executive officers. We currently have no key person insurance on any of our employees.

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. We believe that we currently have adequate levels of insurance for our development and manufacturing activities; however, in the event of one or more large, unforeseen awards, such levels 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.

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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 U.S. law, we may be exposed to various prejudicial actions, including:

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 XOMA or our directors and officers that are predicated upon the civil liability provisions of the U.S. securities laws or entertain original actions brought in Bermuda against XOMA or such persons predicated upon the U.S. 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 XOMA 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.

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Interest Rate Risk

Our exposure to market rate risk for changes in interest rates relates primarily to our investment portfolio. We do not invest in derivative financial instruments. 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.

In February of 2005, we issued $60.0 million of 6.5% convertible senior notes due in 2012.

The table below presents the amounts and related weighted interest rates of our cash equivalents in overnight funds and commercial paper at March 31, 2005 and December 31, 2004:

Under the supervision and with the participation of our management, including our Chairman of the Board, President and Chief Executive Officer and our Vice President, Finance and Chief Financial Officer, we conducted an evaluation of our disclosure controls and procedures, as such term is defined under Rule 13a-14(c) promulgated under the Securities Exchange Act of 1934, as amended, as of the end of the period covered by this report. Based on this evaluation, our Chairman of the Board, President and Chief Executive Officer and our Vice President, Finance and Chief Financial Officer concluded that our disclosure controls and procedures are effective in timely alerting them to material information relating to us and our consolidated subsidiaries required to be included in our periodic SEC filings.

In April of 2003, we implemented a new financial reporting system which represents a significant change in our internal controls. During our evaluation of internal controls conducted for the second quarter of 2003, special procedures were performed regarding the system conversion and implementation. We concluded that the system conversion and implementation was properly controlled to ensure accurate financial reporting. We are further enhancing internal financial controls and staffing consistent with the requirements of the Sarbanes-Oxley Act of 2002. Apart from this, there were no changes in our internal controls over financial reporting during 2005 that have materially affected, or are reasonably likely to materially affect, our internal controls over financial accounting.

Management’s Report on Internal Control over Financial Reporting

Management, including our Chairman of the Board, President and Chief Executive Officer and our Vice President, Finance and Chief Financial Officer, is responsible for establishing and maintaining adequate internal control over financial reporting. The Company’s internal control system was designed to provide reasonable assurance to the Company’s management and board of directors regarding the preparation and fair presentation of published financial statements in accordance with generally accepted accounting principles.

Management assessed the effectiveness of our internal control over financial reporting as of March 31, 2005. In making this assessment, Management used the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission (COSO) in Internal Control—Integrated Framework. Based on our assessment we believe that, as of March 31, 2005, our internal control over financial reporting is effective based on those criteria.

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PART II - OTHER INFORMATION

In November of 2004, a complaint was filed in the United States District Court, Northern District of California, in a lawsuit captioned Physicians Executive Business Corp. v. XOMA Ltd., et al., No. C 04 4878, by an investor in our common shares. The complaint asserts claims for alleged fraud and negligent misrepresentation relating to events preceding the announcement of Phase II trial results for XMP.629 in August of 2004. The complaint seeks unspecified compensatory damages. We filed a motion to dismiss the complaint and that motion was granted with leave to amend on April 27, 2005. Plaintiff has until May 20, 2005, to file an amended complaint. We intend to continue to vigorously defend against this lawsuit.

In April of 2005, a complaint was filed in the Circuit Court of Cook County, Illinois, in a lawsuit captioned Hanna v. Genentech, Inc. and XOMA (US) LLC, No. 2005L00438B, by an alleged participant in one of the clinical trials of RAPTIVA^®. The complaint asserts claims for alleged strict product liability and negligence against Genentech and us based on injuries alleged to have occurred as a result of plaintiff’s treatment in the clinical trial. The complaint seeks unspecified compensatory damages alleged to be in excess of $100,000. Given that this lawsuit was filed only recently, we have not yet fully assessed its merits; However, we intent to vigorously investigate and pursue available defenses.

Sale of $60.0 million principal amount of 6.5% Convertible Senior Notes

On February 7, 2005, we issued $60.0 million of 6.5% convertible senior notes due February 1, 2012 in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The notes are 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 may not redeem the notes. On or after February 6, 2008, we may redeem any or all of the notes at 100% of the principal amount, plus accrued and unpaid interest, if our common shares trade at 150% of the conversion price then in effect for 20 trading days in a 30 consecutive trading day period. Holders of the notes may require 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 as defined in the indenture governing the notes. In addition, following certain fundamental changes, we will increase the conversion rate up to 50 common shares per $1,000 principal amount of notes which would increase the number of shares into which the notes are convertible by up to 3 million common shares or, in lieu thereof, we may, in certain circumstances, elect to adjust the conversion rate and related conversion obligation so that the notes are convertible into shares of the acquiring, continuing or surviving company.

None.

None.

None.

(a) Exhibits:

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XOMA Ltd.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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