EXHIBIT 24.2


        [LETTERHEAD OF MARSHALL, O'TOOLE, GERSTEIN, MURRAY & BORUN]



                               April 9, 1996


Board of Directors
XOMA Corporation
2910 Seventh Street
Berkeley, CA 94710

                  Re:  Registration Statement on Form S-3

Gentlemen:

            Marshall, O'Toole, Gerstein, Murray & Borun hereby consents to
the disclosure of our relationship as patent counsel to XOMA Corporation
(the "Company") in the Company's Registration Statement on Form S-3 (the
"Registration Statement"), and in particular the references to us under the
headings "Risk Factors - No Assurance of Patent Protection/Avoidance of
Patent Infringement" and "Legal Opinions," and to the filing of this
consent as an exhibit to the Registration Statement.

                                    Very truly yours,



                                    Marshall, O'Toole, Gerstein
                                      Murray & Borun