Investor and Media Contacts
XOMA:
Laura Zobkiw
Corporate Communications & Investor Relations
(510) 204-7200
www.xoma.com


               XOMA and Genentech Expand Raptiva(TM) Collaboration
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BERKELEY, CA -- APRIL 10, 2003 -- XOMA Ltd. (Nasdaq: XOMA) announced today that
it has entered into amended and restated agreements relating to all aspects of
its ongoing collaboration with Genentech, Inc. (NYSE: DNA) on Raptiva(TM)
(efalizumab) to reflect the current understanding between the companies. The
agreements include cost sharing, profit sharing and royalty arrangements, as
well as detailed terms relating to participation by Genentech, XOMA and
Genentech's licensees outside the U.S. in the development of all indications for
Raptiva(TM). The agreements also address the ongoing financing by Genentech of
XOMA's share of development and commercialization costs. Key elements of the new
financing arrangements include:

     o    A loan facility to fund XOMA's share of development costs up to $80
          million outstanding at any one time;

     o    Repayment of the development loan, at XOMA's election, in cash, equity
          or through deferral of up to $40 million as an offset against XOMA's
          proceeds from its 25% profit share in the product;

     o    A period of up to 90 days after FDA approval of Raptiva(TM) for XOMA
          to make its election among the repayment options (unless earlier
          repayment is otherwise triggered);

     o    A $15 million loan facility to fund XOMA's share of U.S. marketing and
          sales costs to be repaid in cash within 90 days after FDA approval of
          Raptiva(TM) (unless earlier repayment is otherwise triggered); and

     o    The grant to Genentech of a security interest in XOMA's profit share
          as collateral against any unpaid past due amounts of the loans.

"Much of what is in these new agreements reflects the operating principles that
we and Genentech have been applying for some time," said John L. Castello,
XOMA's chairman, president and chief executive officer, "but we are particularly
pleased to have gained additional flexibility in the financing arrangements.
This is yet another example of the collaborative nature of our relationship with
Genentech."

About XOMA

XOMA develops and manufactures antibody and other protein-based
biopharmaceuticals for disease targets that include cancer, immunological and
inflammatory disorders, and infectious diseases. XOMA's programs include
collaborations: with Genentech, Inc. on the Raptiva(TM) antibody for psoriasis
(BLA submission), rheumatoid arthritis (Phase II), psoriatic arthritis (Phase
II) and other indications; with Baxter Healthcare Corporation to develop


NEUPREX(R) (rBPI(21)) for Crohn's disease (Phase II) and other indications; with
Millennium Pharmaceuticals, Inc. on two biotherapeutic agents, CAB2 and MLN01,
for certain vascular inflammation indications (preclinical); and with Onyx
Pharmaceuticals, Inc. on its ONYX-015 product for various cancers (current
activities suspended, pending partnership discussions). Earlier-stage
development programs include compounds to treat cancer, retinopathies,
autoimmune diseases and infections.

For more information about XOMA's pipeline and activities, please visit XOMA's
website at http://www.xoma.com/.

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Statements contained herein related to the regulatory process and collaborative
arrangements, 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. These risks, including those related to safety
and efficacy of the products being studied; action, inaction or delay by the
U.S. Food and Drug Administration or European regulators; analysis,
interpretation and submission of scientific data; changes in the status of
existing collaborative relationships; the ability of collaborators and other
partners to meet their obligations; and market demand for products, are
described in more detail in XOMA's most recent annual report on Form 10-K and in
other SEC filings.