WHEREVER CONFIDENTIAL INFORMATION IS OMITTED HEREIN (SUCH
OMISSIONS ARE DENOTED BY AN ASTERISK), SUCH CONFIDENTIAL
INFORMATION HAS BEEN SUBMITTED SEPARATELY TO THE SECURITIES AND
EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL
TREATMENT.

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933 AND MAY NOT BE SOLD, OFFERED
FOR SALE, PLEDGED, HYPOTHECATED, ASSIGNED OR OTHERWISE
TRANSFERRED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
STATEMENT UNDER SAID ACT COVERING THE TRANSFER OR AN OPINION OF
COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE COMPANY THAT
SUCH REGISTRATION IS NOT REQUIRED.

THE SECURITIES REPRESENTED HEREBY ARE SUBJECT TO RESTRICTIONS
ON SALE, ASSIGNMENT OR TRANSFER PURSUANT TO THAT CERTAIN COMMON
STOCK AND CONVERTIBLE NOTE PURCHASE AGREEMENT, DATED AS OF
APRIL 22, 1996, BETWEEN THE COMPANY AND GENENTECH, INC., AND
MAY NOT (NOR MAY ANY INTEREST THEREIN) BE SOLD, ASSIGNED,
CONVEYED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF OTHER
THAN IN ACCORDANCE WITH THE PROVISIONS THEREOF.

THE SECURITIES REPRESENTED HEREBY (AND, IF APPLICABLE, ANY
SECURITIES ISSUED UPON CONVERSION THEREOF) MAY BE SUBJECT TO
THE RESTRICTIONS SET FORTH IN THAT CERTAIN COMMON STOCK AND
CONVERTIBLE NOTE PURCHASE AGREEMENT, DATED AS OF APRIL 22,
1996, BETWEEN THE COMPANY AND GENENTECH, INC.

                                           Berkeley, California
                                                  June 13, 1996


                       XOMA CORPORATION

                           AMENDMENT

                              TO

            CONVERTIBLE SUBORDINATED NOTE AGREEMENT


          WHEREAS, XOMA CORPORATION (the "Company") and
GENENTECH, INC. (the "Lender") are parties to that certain
Convertible Subordinated Note Agreement dated April 22, 1996
(the "Original Note Agreement"); and

                              -2-



          WHEREAS, the Company and the Lender desire to amend
the Original Note Agreement as set forth herein;

          NOW, THEREFORE, FOR VALUE RECEIVED, the parties agree
to amend the Original Note Agreement as set forth below.

          1.   Definitions.  Capitalized terms used and not
otherwise defined herein shall have the meanings ascribed to
them in the Original Note Agreement.

          2.   When Certain Loans Payable.  The Original Note
Agreement is hereby amended by adding as a new Section 1(h) the
following:

          (h)  When Certain Loans Payable.  *












          3.   Certain Issuances Treated as Prepayments.  The
Original Note Agreement is hereby amended by deleting the
heading of Section 3(d) thereof and substituting therefor the
heading "Prepayments and Certain Issuances Under Section 4(a)"
and by adding as a new third sentence of Section 3(d) thereof
the following:

     As used herein, prepayments through the issuance of
     Series E Preferred Stock shall include any such
     issuance pursuant to clause * of Section 4(a).

          4.   Automatic Conversion.  The Original Note
Agreement is hereby amended by deleting the first sentence of
Section 4(a) thereof in its entirety and substituting therefor
the following:

          The entire unpaid principal amount of the Note and
     each Tranche under this Note and all unpaid accrued
     interest thereon shall be automatically converted into
     shares of Series E Preferred Stock upon the earliest of

                              -3-



     (i) the date of receipt of Regulatory Approval (as such
     term is defined in the Collaboration Agreement) in the
     United States, (ii) *,

     (iii) with respect to any Tranche (but only that
     Tranche), the date that is ten days after the date that
     the unpaid principal of and unpaid accrued interest on
     such Tranche becomes due and payable, or (iv) *.








          5.   Effect of Amendment.  Except as expressly
amended or modified hereby, the provisions of the Original Note
Agreement shall remain in full force and effect.

          6.   Governing Law.  The parties have agreed that
this amendment will be governed by and construed in accordance
with the laws of the State of Delaware.

          7.   Counterparts.  This amendment may be executed in
two or more counterparts, each of which will be deemed an
original, but all of which together will constitute one and the
same instrument.

          8.   Titles.  The titles of the Sections of this
amendment are inserted for reference only, and are not to be
considered as part of this amendment in construing this
amendment.

          9.   Disputes.  Any disputes under this amendment
will be governed by the provisions of Article 17 of the
Collaboration Agreement.

                              -4-



          IN WITNESS WHEREOF, this amendment has been executed
and delivered on the date first above written by duly
authorized representatives of the Company and the Lender.

                              XOMA CORPORATION



                              By:-------------------------------
                                 Clarence L. Dellio
                                 Senior Vice President,
                                   Operations


                              GENENTECH, INC.



                              By:-------------------------------
                                 Name:
                                 Title: