Investor and Media Contacts:

Laura Zobkiw                                          Peter Davis
Corporate Communications & Investor Relations         Chief Financial Officer
(510) 204-7200                                        (510) 204-7200


                  XOMA Announces Pricing of Public Offering of
          Nine Million Common Shares for Gross Proceeds of $72 Million
          ------------------------------------------------------------

Berkeley, CA - September 19, 2003 -- XOMA Ltd. (NASDAQ: XOMA) today reported
that its previously announced public offering of nine million common shares was
priced at $8.00 per share. The offering is being made from a registration
statement that was filed with the Securities and Exchange Commission on August
13, 2003.

The gross proceeds from the public offering are $72 million. XOMA intends to use
the net proceeds from the offering for general corporate purposes, including
research and development projects, the development or acquisition of new
products or technologies, equipment acquisitions, general working capital and
operating expenses. The Company may also use a portion of the net proceeds of
this offering to repay some or all of the outstanding notes payable to
Genentech, Inc. and Millennium Pharmaceuticals according to existing
collaboration arrangements.

UBS Securities LLC is acting as the sole book running manager in this offering,
and CIBC World Markets Corp., U.S. Bancorp Piper Jaffray, Adams, Harkness &
Hill, Inc., Jefferies & Company, Inc. and ThinkEquity Partners are acting as
co-managers.

XOMA granted to the underwriters an option to purchase 1,350,000 additional
common shares within 30 days after the offering to cover over-allotments.

This press release does not constitute an offer to sell or the solicitation of
an offer to buy any of these securities. This offering of common shares may be
made only by means of a prospectus, a copy of which will be available from UBS
Securities LLC, 299 Park Avenue, New York, New York 10171.

The Company expects to complete the sale of these shares on or about September
24, 2003.

About XOMA

XOMA develops and manufactures antibody and other protein-based
biopharmaceuticals for disease targets that include immunological and
inflammatory disorders, cancer and infectious diseases. XOMA's programs include
collaborations: with Genentech, Inc. on the Raptiva(TM) antibody for psoriasis
(BLA submission), psoriatic arthritis (Phase II) and other indications; and with
Millennium Pharmaceuticals, Inc. on two biotherapeutic agents, CAB-2 and
MLN2201, for vascular inflammation indications (preclinical and phase I,
respectively). Earlier-stage development programs focus on antibodies and other
compounds developed by XOMA for the treatment of cancer, retinopathies and acne.




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Statements made in this press release related 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 actions
by the U.S. Food and Drug Administration, the timing or results of pending or
future clinical trials, changes in the status of the Company's collaborative
relationships, and uncertainties regarding the legal standards applicable to
biotechnology patents, are discussed in the Company's most recent annual report
on Form 10-K and in other SEC filings. Consider such risks carefully in
evaluating XOMA's prospects.