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


              COMMON STOCK AND CONVERTIBLE NOTE PURCHASE AGREEMENT


          THIS COMMON STOCK AND CONVERTIBLE NOTE PURCHASE AGREEMENT
("Agreement"), dated as of April 22, 1996, by and between XOMA CORPORATION, a
Delaware corporation having its principal executive office at 2910 7th Street,
Berkeley, California 94710 (the "Company"), and GENENTECH, INC., a Delaware
corporation having its principal executive office at 460 Point San Bruno
Boulevard, South San Francisco, California 94080 (the "Purchaser").

                                    RECITALS

          A. The parties are entering into a Collaboration Agreement, dated as
of April 22, 1996 (the "Collaboration Agreement"), relating to the development
and marketing of a monoclonal antibody.

          B. In connection with the Collaboration Agreement, the parties desire
that the Purchaser (i) make an investment in the Company through the purchase of
Common Stock, $.0005 par value per share, of the Company (the "Common Stock")
and (ii) fund the Company's development obligations under the Collaboration
Agreement by making certain interest bearing loans to the Company which are to
be evidenced by a Convertible Subordinated Note Agreement in the form attached
hereto as Exhibit A (the "Convertible Note").

          C. Upon the happening of certain events, the Convertible Note shall
automatically convert into shares of a nonvoting convertible preferred stock of
the Company which, in turn, shall be convertible into Common Stock. Such
preferred stock (the "Preferred Stock") shall have the rights, preferences and
privileges as provided in the Certificate of Designation of Convertible
Preferred Stock, Series E, substantially in the form attached as Schedule A to
the form of Convertible Note attached hereto as Exhibit A (the "Certificate of
Designation").

          NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and promises set forth in this Agreement, the parties agree as
follows:

          1. Sale and Purchase of Common Stock. Subject to the terms and
conditions hereof and in reliance upon the representations and warranties
contained herein, the Company will issue and sell to the Purchaser at the
Closing, and the Purchaser will purchase from the Company at the Closing,
1,500,000 shares of Common Stock (the "Shares") for an aggregate purchase price
of $8,842,500 hereinafter referred to as the "Stock Purchase Price."

          2. Sale and Purchase of Convertible Note; Loans. Subject to the terms
and conditions hereof and in reliance upon the representations and warranties
contained herein, the Purchaser will







lend at the Closing the $5,000,000 contemplated to be loaned pursuant to Section
7.1 of the Collaboration Agreement as the initial loan under the Collaboration
Agreement (the "Initial Loan"), and the Purchaser and the Company will execute
and deliver to the Purchaser the Convertible Note (with the initial $5,000,000
loan recorded on Schedule B thereto and designated as "Tranche A" thereunder) to
evidence such initial loan. Subsequent to the Closing, the Purchaser will from
time to time make such additional loans as are contemplated by Section 7.2 of
the Collaboration Agreement and such loans will be evidenced by recording the
date, amount and designation (i.e., "Tranche B," "Tranche C," etc.) thereof on
Schedule B to the Convertible Note as contemplated by the provisions of the
Convertible Note, it being understood and agreed by the parties that in the
event the Collaboration Agreement shall be terminated in accordance with its
terms the Purchaser shall have no further obligation to make any such additional
loans from and after the date of notice of any such termination.

          3. The Closing. The Closing of the purchase and sale of the Shares
hereunder and the making of the Initial Loan and delivery of the Convertible
Note to evidence such loan (the "Closing") shall take place at the offices of
the Purchaser, 460 Point San Bruno Boulevard, South San Francisco, California,
on April 22, 1996 at 8 a.m., local time, or on such other date at such other
time as is mutually agreed upon by the parties (the day on which the Closing
occurs is referenced to herein as the "Closing Date"). At the Closing, the
Company shall deliver to the Purchaser (i) a certificate representing the Shares
and (ii) the Convertible Note, dated as of the Closing Date, against receipt of
the Stock Purchase Price and the Initial Loan by wire transfer of immediately
available funds to the order of the Company.

          4. Representations and Warranties of the Company. The Company hereby
represents and warrants to the Purchaser as follows:

               (a) Corporate Power. The Company is a corporation duly organized,
          validly existing and in good standing under the laws of the State of
          Delaware and is qualified to do business as a foreign corporation in
          each jurisdiction where failure to qualify would have a material
          adverse effect on the business or properties of the Company. The
          Company has full corporate power and authority to own its property, to
          carry on its business as presently conducted and to carry out the
          transactions contemplated hereby.

               (b) Authorization. The Company has full corporate power to
          execute, deliver and perform this Agreement, the Collaboration
          Agreement and the Convertible Note, and each such agreement has been
          duly executed and delivered by the Company and is the legal, valid
          and, assuming due execution by the Purchaser, binding obligation of
          the Company, enforceable in accordance with its terms, subject to
          applicable bankruptcy, insolvency, moratorium, reorganization or
          similar laws affecting creditors' rights generally, and to general
          equitable principles. The execution, delivery and performance by the
          Company of this Agreement, the Collaboration Agreement and the
          Convertible Note, including the borrowing of amounts under the loans
          contemplated by Section 2 hereof and the issuance, sale and delivery
          of the Shares, the Convertible Note, the Preferred Stock and the
          Conversion Shares (as defined in Section 4(c) below) have been duly
          and validly authorized by all necessary corporate action of the
          Company.

               (c) Valid Issuance of Common Stock, Convertible Note and
          Preferred Stock. The Shares, when issued, sold and delivered in
          accordance with the terms hereof for the consideration expressed
          herein, will be duly authorized, validly issued, fully paid and non-


                                       -2-





         assessable, and, based in part upon the representations of the
         Purchaser in this Agreement, will be issued in compliance with all
         applicable federal and state securities laws. The Convertible Note,
         when issued, sold and delivered in accordance with the terms hereof for
         the consideration expressed herein, will be duly authorized and validly
         issued, and, based in part upon the representations of the Purchaser in
         this Agreement, will be issued in compliance with all applicable
         federal and state securities laws. The Preferred Stock, after giving
         effect to the filing of the Certificate of Designation with the
         Secretary of State of the State of Delaware as contemplated by Section
         8, and any shares of Common Stock issued upon conversion of such
         Preferred Stock in accordance with the terms thereof (the "Conversion
         Shares"), will be duly authorized, validly issued, fully paid and
         non-assessable and, based in part upon the representations of the
         Purchaser in this Agreement, will be issued in compliance with all
         applicable federal and state securities laws.

               (d) Governmental Approvals. Based in part on the representations
          made by the Purchaser in Sections 5 and 6, no authorization, consent,
          approval, license, exemption of or filing or registration with any
          court or governmental department, commission, board, bureau, agency or
          instrumentality, domestic or foreign, under any applicable laws, rules
          or regulations presently in effect, is or will be necessary to be made
          or obtained by the Company for, or in connection with, the execution
          and delivery of this Agreement, the Collaboration Agreement or the
          Convertible Note or consummation of the transactions contemplated
          hereby or thereby or performance by the Purchaser of its obligations
          hereunder or thereunder, except for (i) the filing of the Certificate
          of Designation as contemplated by Section 8, (ii) such other filings
          under applicable securities laws which will be made by the Company
          within the prescribed periods, including the filing by the Company of
          a notice under Section 25102(f) of the California Codes, as amended,
          and the payment of any fee relating thereto, (iii) any of the
          foregoing required or contemplated to be made in accordance with
          Section 9 and (iv) any of the foregoing required in connection with
          the conversion of the Preferred Stock.

               (e) Litigation. Except as disclosed in the SEC Reports (as
          defined in Section 4(j) below), there is no litigation or governmental
          proceeding or investigation pending or, to the knowledge of the
          Company, threatened against the Company which would materially and
          adversely affect (i) the execution and delivery of this Agreement, the
          Collaboration Agreement or the Convertible Note, or (ii) the
          performance by the Company of its obligations hereunder or thereunder.

               (f) Subsidiaries. The Company has no active subsidiaries and does
          not otherwise directly or indirectly control any other business
          entity. The Company has furnished the Purchaser with true, correct and
          complete copies of its Amended and Restated Certificate of
          Incorporation and Bylaws, together with any amendments thereto as of
          the date hereof.

               (g) Absence of Certain Developments. Since the date of its most
          recent report filed with the Securities and Exchange Commission (the
          "Commission") pursuant to the Securities and Exchange Act of 1934, as
          amended from time to time (such act, together with the rules and
          regulations promulgated thereunder, the "Exchange Act"), except as
          disclosed therein, there has been no (i) material adverse change in
          the condition, financial or otherwise, of the Company or its assets,
          liabilities, properties, business, operations or prospects generally,
          (ii) declaration, setting aside or payment of any dividend or other
          distribution with respect to the capital stock of the Company, or
          (iii) loss, destruction or damage to any property of the


                                       -3-





         Company, whether or not insured, which has or may have a material
         adverse effect on the Company.

                  (h) Absence of Undisclosed Liabilities. Except as and to the
         extent reflected or stated in the SEC Reports and except for the
         issuance of the Company's Non-Voting Cumulative Convertible Preferred
         Stock, Series D, the Company has no material accrued or contingent
         liability of a type required to be reflected on a balance sheet in
         accordance with generally accepted accounting principles or described
         in the footnotes thereto, other than liabilities arising in the
         ordinary course of its business since the SEC Reports, arising out of
         any transaction or state of facts existing prior to the date hereof.

               (i) Non-Contravention. The execution, delivery and performance by
          the Company of this Agreement, the Collaboration Agreement and the
          Convertible Note (i) do not and will not contravene or conflict with
          the Amended and Restated Certificate of Incorporation or Bylaws of the
          Company and (ii) do not contravene or conflict with or, based in part
          on the representations made by the Purchaser in Sections 5 and 6 and
          assuming satisfaction of the requirements referenced in Section 4(d),
          constitute a violation of any provision of any law, regulation,
          judgment, injunction, order or decree binding upon or applicable to
          the Company, or result in a breach of or constitute a default under
          any material agreement of the Company (whether upon notice or passage
          of time), in any manner which would materially and adversely affect
          the Purchaser's rights or its ability to realize the intended benefits
          to it under this Agreement, the Collaboration Agreement or the
          Convertible Note.

               (j) Filings. The Company has filed in a timely manner, and has
          delivered to the Purchaser copies of, the following reports required
          to be filed with the Commission under the Exchange Act: (i) the
          Company's annual report on Form 10-K for the fiscal year ended
          December 31, 1995, as amended by Amendment No. 1 on Form 10-K/A, and
          (ii) all of its other reports (including without limitation reports on
          Form 8-K), statements, schedules and registration statements filed
          with the Commission since December 31, 1995. As of its filing date, no
          such report or statement filed pursuant to the Exchange Act contained
          any untrue statement of a material fact or omitted to state any
          material fact necessary in order to make the statements made therein,
          in the light of the circumstances under which they were made, not
          misleading. The Company has also delivered to the Purchaser a copy of
          the Company's preliminary Proxy Statement (filed with the Commission
          on April 12, 1996) prepared in connection with its 1996 annual meeting
          of stockholders (such preliminary Proxy Statement and the Company's
          annual report on Form 10-K for the year ended December 31, 1995, as
          amended, are referred to herein as the "SEC Reports").

               (k) No Brokers. The Company has not directly or indirectly
          employed any broker, finder or other person (including any employee)
          that might be entitled to a fee, commission or other compensation upon
          the execution of this Agreement, the Collaboration Agreement or the
          Convertible Note or the consummation of the transactions contemplated
          by this Agreement, the Collaboration Agreement or the Convertible Note
          for which the Purchaser or the Company is or may be liable.

               (l) Registration Rights. The Company is not, and will not become
          during the term of this Agreement, a party to any contract, agreement
          or understanding providing for the registration of its securities
          under federal or state securities laws that restricts, limits,
          prohibits


                                       -4-





         or conflicts or would restrict, limit, prohibit or conflict with the
         registration rights granted to the Purchaser pursuant to Section 10
         hereof.

          5. Representations and Warranties of the Purchaser. The Purchaser
hereby represents and warrants to the Company as follows:

               (a) Corporate Power. The Purchaser is a corporation duly
          organized, validly existing and in good standing under the laws of the
          State of Delaware. The Purchaser has full corporate power and
          authority to carry on its business as presently conducted and to carry
          out the transactions contemplated hereby.

               (b) Authorization. The Purchaser has full corporate power to
          execute, deliver and perform this Agreement, the Collaboration
          Agreement and the Convertible Note, and each such agreement has been
          duly executed and delivered by the Purchaser and is the legal, valid
          and, assuming due execution by the Company, binding obligation of the
          Purchaser, enforceable in accordance with its terms, subject to
          applicable bankruptcy, insolvency, moratorium, reorganization or
          similar laws affecting creditors' rights generally, and to general
          equitable principles. The execution, delivery and performance by the
          Purchaser of this Agreement, the Collaboration Agreement and the
          Convertible Note, including the purchase of the Shares and the loans
          contemplated by Section 2 hereof pursuant to the Convertible Note,
          have been duly and validly authorized by all necessary corporate
          action of the Purchaser.

               (c) Litigation. There is no litigation or governmental proceeding
          or investigation pending or, to the knowledge of the Purchaser,
          threatened against the Purchaser which would materially and adversely
          affect (i) the execution and delivery by the Purchaser of this
          Agreement, the Collaboration Agreement or the Convertible Note, or
          (ii) the performance by the Purchaser of its obligations hereunder or
          thereunder.

               (d) No Brokers. The Purchaser has not directly or indirectly
          employed any broker, finder or other person (including any employee)
          that might be entitled to a fee, commission or other compensation upon
          the execution of this Agreement, the Collaboration Agreement or the
          Convertible Note or the consummation of the transactions contemplated
          by this Agreement, the Collaboration Agreement or the Convertible Note
          for which the Purchaser or the Company is or may be liable.


          6. Compliance with Securities Laws and Restrictions on Transfer of
Securities.

               (a) The Purchaser hereby represents and warrants to, and agrees
          with, the Company as follows:

                    (i) The Purchaser (A) is purchasing the Shares and the
               Convertible Note (including the making of the Initial Loan and
               each subsequent loan pursuant to Section 7.2 of the Collaboration
               Agreement), (B) will acquire the Preferred Stock upon conversion
               of the Convertible Note (in the event of any such conversion),
               and (C) will acquire the Conversion Shares upon conversion of the
               Preferred Stock (in the event of any such conversion) (the
               Shares, Convertible Note, Preferred Stock and Conversion Shares
               are referred to herein, collectively, as the "Securities") for
               its own account for


                                       -5-





               investment only and not with a view to any resale or distribution
               thereof, except pursuant to an effective registration statement
               under the Securities Act of 1933, as amended from time to time
               (such act, together with the rules and regulations promulgated
               thereunder, the "Securities Act"), covering the sale, assignment
               or transfer or an opinion of counsel in form and substance
               satisfactory to the Company that such registration is not
               required.

                    (ii) The Purchaser has received and carefully reviewed the
               SEC Reports, and has had the opportunity to obtain and receive
               such other information as it deems necessary to understand the
               business and financial condition of the Company and to make the
               investment decision to purchase the Securities.

                    (iii) As an investor in companies in the biopharmaceutical
               industry and a participant in such industry, the Purchaser has
               such knowledge and experience in financial and business matters
               that it is capable of evaluating the merits and risks of the
               investment represented by the Securities, and it is able to bear
               the economic risk of such investment.

                    (iv) The Purchaser understands that the Securities are
               being, or will be, sold or issued in a transaction which is
               exempt from the registration requirements of the Securities Act
               by reason of the provisions of Section 4(2) of the Securities Act
               (or Section 3(a)(9) of the Securities Act in the case of the
               issuance of the Preferred Stock and the Conversion Shares upon
               conversion of the Convertible Note and the Preferred Stock,
               respectively), and that such Securities will be subject to
               transfer restrictions and must be held indefinitely unless
               subsequently registered under the Securities Act or an exemption
               from such registration is available.

                           The certificates representing the Securities will be
                  affixed with a legend reading as follows:

                    "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."

                    Except as set forth in Section 14 hereof, the restrictions
               on sale, assignment and transfer of the Shares, the Preferred
               Stock and the Conversion Shares contained in this Section
               6(a)(iv) shall terminate at such time as there shall be delivered
               to the Company and the Purchaser an opinion of counsel to the
               Purchaser, in form and substance satisfactory to the Company, to
               the effect that, due to the lapse of time or otherwise, no
               registration of such securities is required under the Securities
               Act in connection with any distribution of such securities to the
               public in the United States. In addition, at any time after (A)
               the delivery of such opinion; (B) such securities are sold
               pursuant to and in accordance with an effective registration
               statement under the Securities Act covering such sale; or (C) the
               Purchaser shall have delivered to the


                                       -6-





               Company a written undertaking, executed by the Purchaser and any
               institution currently executing or proposing to execute sales of
               such securities, to the effect that such sales shall be made only
               in compliance with all applicable provisions of Rule 144 under
               the Securities Act (or any applicable similar rule which may be
               promulgated from time to time), the Purchaser shall be entitled
               to exchange its certificate representing such securities (or any
               portion thereof as to which (A), (B) or (C) above applies) for
               new certificates not bearing the legend set forth in Section
               6(a)(iv).

          (b) The Purchaser may only sell, assign or transfer all or a portion
of the Convertible Note to a wholly-owned subsidiary or to F. Hoffmann-LaRoche
Ltd or any of its Affiliates (as defined in Section 7(b)) (the "Roche
Affiliates") which are directly or indirectly controlled by it (collectively,
with such Roche Affiliates, "Roche") (so long as Roche owns at least a majority
of the outstanding Voting Stock (as such term is defined in Section 7(a)) of the
Purchaser, provided that (i), in the case of a wholly-owned subsidiary, such
subsidiary agrees with the Purchaser and the Company in writing to rescind such
transaction in the event it ceases to be a wholly-owned subsidiary of the
Purchaser and agrees in writing with the Company to comply with all the
provisions of this Agreement applicable to the Purchaser and, in the case of the
Convertible Note, to be bound by the obligations of the "Lender" thereunder
(including the corresponding obligations under the Collaboration Agreement), and
(ii), in the case of Roche, Roche agrees with the Purchaser and the Company in
writing to rescind such transaction in the event it ceases to be the owner of at
least a majority of the outstanding Voting Stock of the Purchaser and agrees in
writing with the Company to comply with all of the provisions of this Agreement
applicable to the Purchaser and, in the case of the Convertible Note, to be
bound by the obligations of the "Lender" thereunder (including the corresponding
obligations under the Collaboration Agreement). Notwithstanding any such sale,
assignment or transfer, the Purchaser shall not be relieved of its obligations
hereunder or under the Convertible Note or the Collaboration Agreement. The
Purchaser agrees that the Preferred Stock shall not be sold, assigned or
transferred (either in whole or in part) to a third party who is not an
Affiliate (as such term is defined in Section 7(b) hereof) and is not Roche,
except if as a condition of such sale, assignment or transfer the Preferred
Stock shall automatically be converted into Conversion Shares.

          (c) Notwithstanding any provision of this Agreement to the contrary,
other than as permitted by, and in accordance with, the provisions of Section
6(b), without the prior written consent of the Company, the Purchaser may not
sell, assign, convey, pledge, hypothecate or otherwise dispose of the
Convertible Note (representing any and all loans outstanding as contemplated by
Section 2) or any interest therein. Accordingly, the Convertible Note will be
affixed with a legend reading as follows:

               "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."



                                       -7-





          (d) The Purchaser understands that notations restricting the transfer
of the Securities will be made on the transfer records of the Company and that a
stop transfer order will be entered with the Company's transfer agent.

          (e) None of the Securities (nor any interest therein) shall be sold,
assigned or offered except in accordance with the provisions of this Section 6.

          7. Additional Covenants of Purchaser Regarding Securities.

          (a) Effectiveness and Termination. The provisions of Sections 7(b)
through 7(d) shall become effective at such time (if any), and from time to
time, as the Purchaser and its Affiliates, taken together, own Voting Stock of
the Company (which includes the Common Stock) representing ten percent (10%) or
more of the total outstanding Voting Stock of the Company, and shall continue in
effect until the earlier of (i) the fifteenth anniversary of the date of this
Agreement or (ii) such time as the Purchaser and its Affiliates, taken together,
own less than ten percent (10%) of the total outstanding Voting Stock of the
Company, provided that such Sections shall again become effective if, and at
such time, and from time to time, as the Purchaser and its Affiliates, taken
together, own such percentage of Voting Stock of the Company within the fifteen
year period commencing on the date hereof. For purposes of this Agreement, the
term "Voting Stock" means the equity securities (as such term is used in the
Exchange Act) having the ordinary power to vote in the election of directors of
the issuer thereof (other than securities having such power only upon the
happening of a contingency). For purposes of this Section 7, owned Voting Stock
shall include Voting Stock, securities directly or indirectly convertible into
or exchangeable for Voting Stock (whether or not subject to a contingency), and
rights to acquire any of the foregoing. The provisions of Sections 7(b) through
7(d) shall have no effect unless and until they become effective, and only so
long as they are effective, pursuant to this Section 7(a), other than for
purposes of defining certain terms used elsewhere in this Agreement.
Notwithstanding any provision hereof to the contrary, this Section 7 shall not
apply to any Preferred Stock, Shares or Conversion Shares assigned, sold or
transferred in accordance with Section 6(a)(iv), and the legend required to be
affixed to the certificates representing such shares pursuant to Section 7(d)
shall be removed upon any such assignment, sale or transfer of such shares.

          (b) Additional Stock Purchases by Purchaser. The Purchaser hereby
agrees that neither the Purchaser nor any of its Affiliates nor anyone acting on
its or their behalf will acquire any equity securities (as such term is used in
the Exchange Act) of the Company without the Company's prior written approval,
except as contemplated by this Agreement or pursuant to the Convertible Note or
the Preferred Stock. For purposes of this Agreement, the term "Affiliate" means,
when used with respect to any specified person, any other person directly or
indirectly controlled by such specified person. For the purposes of this
definition, "control," when used with respect to any person, means the power to
direct the management and policies of such person, directly or indirectly,
whether through the ownership of voting securities, by contract or otherwise,
and the terms "affiliated" and "controlled" have meanings correlative to the
foregoing. The obligations of this Section 7(b) shall terminate if another
person or group has acquired Voting Stock of the Company (or rights to acquire
Voting Stock of the Company) which results in such person or group owning or
having the right to acquire Voting Stock of the Company with aggregate voting
power of more than 50% of the total voting power of the Company then in effect.


                                       -8-






          (c) Solicitation of Proxies; Participation in Control Contests.
Without the Company's prior written consent, (i) the Purchaser shall not solicit
proxies with respect to any Voting Stock of the Company, nor shall it become a
"participant" in any "election contest" (as such terms are used under Regulation
14A of the Exchange Act) relating to the election of directors of the Company;
and (ii) the Purchaser shall not, and shall cause its Affiliates not to (and the
Purchaser and such Affiliates shall not together or in conjunction with third
parties who are not Affiliates form a "group" (as used under Regulation 13D/G of
the Exchange Act), act in concert, or encourage other persons to), directly or
indirectly, acquire or offer to acquire, seek, propose or agree to acquire,
whether by means of a purchase, agreement, business combination or any other
manner, beneficial ownership of any securities or assets of the Company
(including options to acquire such ownership) seeking or proposing to influence,
advise, change or control the management, Board of Directors, governing
instruments or policies or affairs of the Company. Subject only to this Section
7(c), the Purchaser shall be entitled to vote its shares of Voting Stock of the
Company in its discretion.

          (d) Restrictive Legends. In addition to any restrictive legends
required by Section 6, subject to the penultimate and last sentences of Section
7(a), the certificates representing the Securities will be affixed with a legend
reading as follows:

                    "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."

          8. Additional Covenants of the Company.

          (a) Filing of Certificate of Designation. The Company shall file with
the Secretary of State of the State of Delaware the Certificate of Designation
not later than the Closing Date.

          (b) Stockholders' Rights Plan. The Company agrees that, as long as the
Purchaser is substantially in compliance with the terms of this Agreement, the
Collaboration Agreement and the Securities, (i) the Purchaser will not be
declared an Adverse Person for purposes of the Stockholder Rights Agreement
dated as of October 27, 1993 between the Company and First Interstate Bank of
California, as rights agent (the "Rights Agreement"), and (ii) the Company will
take all commercially reasonable efforts to redeem the preferred stock purchase
rights which may be distributed under the Rights Agreement if the Purchaser
becomes an Acquiring Person (as defined in the Rights Agreement) and the Stock
Acquisition Date (as defined in the Rights Agreement) has occurred.

          9. Conditions to Closing.

          (a) Conditions to Purchaser's Obligations at the Closing. The
Purchaser's obligation to purchase and pay for the Shares and make the Initial
Loan at the Closing is


                                       -9-





subject to the fulfillment on or prior to the Closing of the following
conditions, any one or more of which may be waived in whole or in part by the
Purchaser:

               (i) Compliance with Laws. At the Closing, the purchase of the
          Shares hereunder and the loans to be made by the Purchaser pursuant to
          the Convertible Note shall be legally permitted by all laws and
          regulations to which the Purchaser or the Company is subject.

               (ii) Representations and Warranties. Each of the representations
          and warranties of the Company set forth in Section 4 shall be true and
          correct as if made on the Closing Date.

               (iii) Performance. The Company shall have performed and complied
          with all agreements, obligations and conditions contained in this
          Agreement that are required to be performed or complied with by it on
          or before the Closing Date, including delivery of the Shares.

               (iv) Compliance Certificate. The Senior Vice President,
          Operations of the Company shall deliver to the Purchaser on the
          Closing Date a certificate certifying that the conditions set forth in
          clauses (ii) and (iii) of this Section 9(a) have been fulfilled.

               (v) Other Agreements. The Company shall have executed and
          delivered to the Purchaser the Collaboration Agreement and the
          Convertible Note.

               (vi) Consents. The Company and the Purchaser shall have obtained
          all consents (including all governmental and regulatory consents,
          approvals, or authorizations required in connection with the valid
          execution and delivery of this Agreement, the Collaboration Agreement
          and the Convertible Note), permits and waivers necessary or required
          to be obtained on or prior to the Closing Date for consummation of the
          transactions contemplated hereby.

               (vii) Opinion of Counsel to the Company. The Purchaser shall have
          received from Cahill Gordon & Reindel, special counsel for the
          Company, an opinion dated as of the Closing Date, substantially in the
          form set forth in Exhibit B attached hereto.

               (viii) Proceedings and Documents. All corporate and other
          proceedings in connection with the transactions contemplated in
          connection with the purchase of the Shares and the Initial Loan and
          all documents incident thereto (including the issuance of the
          Preferred Stock and the Conversion Shares) shall be reasonably
          satisfactory in form and substance to the Purchaser and the
          Purchaser's counsel, and they shall have received all such counterpart
          original and certified or other copies of such documents as they may
          reasonably request.

          (b) Conditions to Company's Obligations at the Closing. The Company's
obligation to sell and issue the Shares and execute and deliver the Convertible
Note at the Closing is subject to the fulfillment on or prior to the Closing of
the following conditions, any one or more of which may be waived in whole or in
part by the Company:


                                      -10-






               (i) Compliance with Laws. At the Closing, the purchase of the
          Shares hereunder and the loans to be made by the Purchaser shall be
          legally permitted by all laws and regulations to which the Purchaser
          or the Company is subject.

               (ii) Representations and Warranties. Each of the representations
          and warranties of the Purchaser set forth in Sections 5 and 6 shall be
          true and correct as if made on the Closing Date.

               (iii) Payment of Purchase Price. The Purchaser shall have
          delivered to the Company payment of the Stock Purchase Price and the
          Initial Loan in accordance with Section 3 hereof.

               (iv) Performance. The Purchaser shall have performed and complied
          with all agreements, obligations and conditions contained in this
          Agreement that are required to be performed or complied with on or
          before the Closing Date.

               (v) Other Agreements. The Purchaser shall have executed and
          delivered to the Company the Collaboration Agreement and the
          Convertible Note.

               (vi) Consents. The Company and the Purchaser shall have obtained
          all consents (including all governmental and regulatory consents,
          approvals, or authorizations required in connection with the valid
          execution and delivery of this Agreement, the Collaboration Agreement
          and the Convertible Note), permits and waivers necessary or required
          to be obtained on or prior to the Closing Date for consummation of the
          transactions contemplated hereby.

               (vii) Proceedings and Documents. All corporate and other
          proceedings in connection with the transactions contemplated in
          connection with the purchase of the Shares and the Initial Loan and
          all documents incident thereto (including the issuance of the
          Preferred Stock and the Conversion Shares) shall be reasonably
          satisfactory in form and substance to the Company and the Company's
          counsel, and they shall have received all such counterpart original
          and certified or other copies of such documents as they may reasonably
          request.

          10. Registration Rights.

          (a) Certain Definitions. As used in this Agreement, the following
terms shall have the following respective meanings:

               "Holder" shall mean the Purchaser or transferee of the Purchaser
which is a holder of Registrable Securities and acquired such shares in
accordance with Section 6(b).

               "Prospectus" shall mean the prospectus included in any
Registration Statement (including, without limitation, a prospectus that
discloses information previously omitted from a prospectus filed as part of an
effective registration statement in reliance upon Rule 430A promulgated pursuant
to the Securities Act), as amended or supplemented by any prospectus supplement,
with respect to the terms of the offering of any portion of the Registrable
Securities covered by such Registration Statement, and all other amendments and
supplements


                                      -11-





to any such prospectus, including post-effective amendments, and all materials
incorporated by reference or deemed to be incorporated by reference, if any, in
such prospectus.

               "Registrable Securities" shall mean (i) the Shares issued to the
Purchaser at the Closing, (ii) the Conversion Shares of the Company issued upon
conversion of the Preferred Stock issued upon conversion of the Convertible Note
and (iii) any Common Stock of the Company issued in respect of such shares as a
result of any stock split, stock dividend or recapitalization.

               "Registration Expenses" shall mean all expenses incurred by the
Company in complying with Sections 10(b) through (d), including, without
limitation, all registration, qualification and filing fees, printing expenses,
escrow fees, fees and disbursements of counsel for the Company, blue sky fees
and expenses, and the expense of any special audits incident to or required by
any such registration (but excluding the compensation of regular employees of
the Company which shall be paid in any event by the Company).

               "Registration Statement" shall mean any registration statement of
the Company that covers any of the Registrable Securities pursuant to the
provisions of this Agreement, including the Prospectus, amendments and
supplements to such registration statement or Prospectus, including pre- and
post-effective amendments, all exhibits thereto, and all material incorporated
by reference or deemed to be incorporated by reference, if any, in such
registration statement.

          (b) Shelf Registration Statements.

               (i) The Company agrees to file with the Commission, promptly
          following the Closing, but in no event later than 45 days after the
          Closing, a Registration Statement for an offering to be made on a
          continuous basis pursuant to Rule 415 of the Securities Act (a "Shelf
          Registration Statement") covering all of the Shares and any
          Registrable Securities issued in respect of such Shares. Such Shelf
          Registration Statement shall be on Form S-3 under the Securities Act
          or another appropriate form permitting registration of such Shares and
          any Registrable Securities issued in respect of such Shares for resale
          by the Holder in the manner or manners reasonably designated by the
          Holder. The Company shall use its commercially reasonable efforts to
          cause such Shelf Registration Statement to be declared effective
          pursuant to the Securities Act as promptly as practicable following
          the filing thereof and to keep it continuously effective under the
          Securities Act until termination of such obligation pursuant to
          Section 10(f)(i).

               (ii) The Company agrees to file with the Commission, promptly
          following the Conversion Date (as such term is defined in the
          Convertible Note Agreement) first occurring, but in no event later
          than 45 days after the Conversion Date, a Shelf Registration Statement
          covering all of the Conversion Shares and any Registrable Securities
          issued in respect of such Conversion Shares. Such Shelf Registration
          Statement shall be on Form S-3 under the Securities Act or another
          appropriate form permitting registration of such Conversion Shares and
          any Registrable Securities issued in respect of such Conversion Shares
          for resale by the Holder in the manner or manners reasonably
          designated by the Holder. The Company shall use its


                                      -12-





          commercially reasonable efforts to cause such Shelf Registration
          Statement to be declared effective pursuant to the Securities Act as
          promptly as practicable following the filing thereof and to keep it
          continuously effective under the Securities Act until termination of
          such obligation pursuant to Section 10(f)(ii).

          (c) Certain Notices; Suspension of Sales. The Holder agrees that, upon
receipt of any notice from the Company of the happening of any event of the kind
described in any of clauses (w) through (z) of Section 10(d)(iii) (with, if
requested by the Holder, a description in reasonable detail thereof), the such
Holder will forthwith discontinue disposition of the Registrable Securities
covered by such Registration Statement or Prospectus until the Holder's receipt
of copies of the supplemented or amended Prospectus contemplated by Section
10(d)(v), or until it is advised in writing (the "Advice") by the Company that
the use of the applicable Prospectus may be resumed, and, in either case, has
received copies of any additional or supplemental filings that are incorporated
or deemed to be incorporated by reference in such Prospectus.

          (d) Registration Procedures. In connection with the Company's
registration obligations under Section 10(b), the Company shall with respect to
each Shelf Registration Statement:

               (i) Prepare and file with the Commission such amendments,
          including post-effective amendments, to each Registration Statement as
          may be necessary to keep such Registration Statement continuously
          effective for the applicable time period set forth in, and subject to,
          Section 10(b); cause the related Prospectus to be supplemented by any
          required Prospectus supplement, and as so supplemented to be filed
          pursuant to Rule 424 (or any similar provisions then in force) under
          the Securities Act and the Exchange Act with respect to the
          disposition of all securities covered by such Registration Statement
          during such period in accordance with the intended methods of
          disposition by the Holder set forth in such Registration Statement as
          so amended or in such Prospectus as so supplemented, provided such
          Holder complies with the information requirements of Section 10(h).

               (ii) Deliver to the Holder, without charge, as many copies of the
          Prospectus or Prospectuses (including each form of prospectus) and
          each amendment or supplement thereto it reasonably requests; and,
          subject to Section 10(c), the Company hereby consents to the use of
          such Prospectus and each amendment or supplement thereto by the Holder
          in connection with the offering and sale of the covered Shares,
          Conversion Shares or Registrable Securities, as the case may be,
          covered by such Prospectus and any amendment or supplement thereto,
          provided that no Holder shall be entitled to use the Prospectus unless
          and until such Holder shall have furnished to the Company any required
          information pursuant to Section 10(h).

               (iii) Notify the Holder (v) when a Prospectus or any Prospectus
          supplement or post-effective amendment is proposed to be filed, and,
          with respect to a Registration Statement or any post-effective
          amendment, when the same has become effective, (w) of any request of
          the Commission or any other Federal or state governmental authority
          for amendments or supplements to a Registration Statement or related
          Prospectus or for additional information related thereto, (x) of the
          issuance by the


                                      -13-





          Commission, any state securities commission, any other governmental
          agency or any court of any stop order, order or injunction suspending
          or enjoining the use or the effectiveness of a Registration Statement
          or the initiation of any proceedings for that purpose, (y) of the
          receipt by the Company of any notification with respect to the
          suspension of the qualification or exemption from qualification of any
          of the Shares, Conversion Shares or Registrable Securities, as the
          case may be, for sale in any jurisdiction, or the initiation or
          threatening of any proceeding for such purpose, and (z) of the
          existence of any fact and the happening of any event that makes any
          statement made in such Registration Statement or related Prospectus or
          any document incorporated or deemed to be incorporated therein by
          reference untrue in any material respect, or that requires the making
          of any changes in such Registration Statement, Prospectus or document
          so that in the case of the Registration Statement, it will not contain
          any untrue statement of a material fact or omit to state any material
          fact required to be stated therein or necessary to make the statements
          therein not misleading and that, in the case of the Prospectus, such
          Prospectus will not contain any untrue statement of a material fact or
          omit to state any material fact required to be stated therein or
          necessary to make the statements therein, in light of the
          circumstances under which they were made, not misleading.

               (iv) Use its commercially reasonable efforts (which shall include
          appropriate responses to any requests of the type described in clause
          (w) of Section 10(d)(iii)) to avoid the issuance of, or, if issued,
          obtain the withdrawal of any order enjoining or suspending the use or
          effectiveness of a Registration Statement or the lifting of any
          suspension of the qualification (or exemption from qualification) of
          any of the covered Registrable Securities for sale in any
          jurisdiction, at the earliest practicable moment.

               (v) Upon the occurrence of any event contemplated by clause (z)
          of Section 10(d)(iii), as promptly as practicable but in no event
          later than 60 days thereafter, prepare a supplement or amendment,
          including, if appropriate, a post-effective amendment, to each
          Registration Statement or a supplement to the related Prospectus or
          any document incorporated or deemed to be incorporated therein by
          reference, and file any other required document so that, as thereafter
          delivered, such Prospectus will not contain an untrue statement of a
          material fact or omit to state a material fact required to be stated
          therein or necessary to make the statements therein, in light of the
          circumstances under which they were made, not misleading.
          Notwithstanding anything herein to the contrary, nothing herein shall
          require the Company to prepare and file any such supplement or
          amendment if the Company shall determine in its reasonable judgment
          that compliance with the requirements hereof would require the
          disclosure of non-public material corporate developments, the
          disclosure of which in the reasonable judgment of the Company would be
          adverse to the interests of the Company, and the obligations of the
          Company to prepare and file any such supplements or amendments shall
          be suspended until such time as such non-public developments otherwise
          become publicly known or announced or would not be required to be so
          disclosed in connection therewith, provided that if as a consequence
          of any delay in the filing of any supplement or amendment, the Holder
          is prevented from effecting sales under the Registration Statement for
          more than thirty (30)


                                      -14-





          consecutive days, if requested by the Holder, the Company's
          determination shall have been confirmed by a determination by the
          Board of Directors of the Company.

               (vi) Use its commercially reasonable efforts to register or
          qualify, or cooperate with the Holder in connection with the
          registration or qualification (or exemption from such registration or
          qualification), of the Shares, Conversion Shares or Registrable
          Securities, as the case may be, for offer and sale under the
          securities or Blue Sky laws of such jurisdictions within the United
          States as the Holder reasonably requests in writing, keep each such
          registration or qualification (or exemption therefrom) effective
          during the period such Registration Statement is required to be kept
          effective and do any and all other acts or things necessary or
          advisable to enable the disposition in such jurisdictions of the
          Shares, Conversion Shares or Registrable Securities, as the case may
          be, covered by the applicable Registration Statement; provided,
          however, that the Company shall not be required to qualify generally
          to do business in any jurisdiction where it is not then so qualified
          or take any action that would subject it to general service of process
          in any such jurisdiction where it is not then so subject or subject
          the Company to any tax in any such jurisdiction where it is not then
          so subject.

               (vii) Comply with applicable rules and regulations of the
          Commission and make generally available to its security holders
          earning statements satisfying the provisions of Section 11(a) of the
          Securities Act and Rule 158 thereunder (or any similar rule
          promulgated under the Securities Act), no later than 60 days after the
          end of any 12-month period (or 90 days after the end of any 12-month
          period if such period is a fiscal year), commencing on the first day
          of the first fiscal quarter after the effective date of a Registration
          Statement, which statement shall cover said period, consistent with
          the requirements of Rule 158.

               (viii) List all Shares, Conversion Shares and Registrable
          Securities covered by such Registration Statement on any securities
          exchange on which the Common Stock is then listed or authorize for
          quotation on the National Association of Securities Dealers Automated
          Quotation System ("Nasdaq") or the Nasdaq National Market all Shares,
          Conversion Shares and Registrable Securities covered by such
          Registration Statement if the Common Stock is then so authorized for
          quotation.

          (e) Expenses of Registration. All Registration Expenses incurred in
connection with any registration, qualification or compliance by the Company
pursuant to Sections 10(b), (c) or (d) of this Agreement shall be borne by the
Company.

          (f) Termination of Registration Rights.

               (i) The registration obligations of the Company pursuant to
          Sections 10(b) through (d) of this Agreement shall terminate with
          respect to the Shelf Registration Statement contemplated by Section
          10(b)(i) at the time at which all of the Shares, Conversion Shares and
          Registrable Securities required to be covered by such Registration
          Statement can be sold within a given three-month period without
          compliance with the registration requirements of the Securities Act
          pursuant to Rule 144 or other applicable exemption supported by a
          written opinion of legal counsel for


                                      -15-





          the Company which shall be reasonably satisfactory in form and
          substance to legal counsel for Holder.

               (ii) The registration obligations of the Company pursuant to
          Sections 10(b) through (d) of this Agreement shall terminate with
          respect to the Shelf Registration Statement contemplated by Section
          10(b)(ii) at the time at which all of the Registrable Securities
          required to be covered by such Registration Statement may be sold
          within a given three-month period without compliance with the
          registration requirements of the Securities Act pursuant to Rule 144
          or other applicable exemption supported by a written opinion of legal
          counsel for the Company which shall be reasonably satisfactory in form
          and substance to legal counsel for Holder.

          (g) Indemnification.

               (i) The Company agrees to indemnify and hold harmless (A) the
          Holder, (B) each person, if any, who controls (within the meaning of
          Section 15 of the Securities Act or Section 20 of the Exchange Act)
          the Holder (any of the persons referred to in this clause (B) being
          hereinafter referred to as a "controlling person"), and (C) the
          respective officers, directors, partners, employees, representatives
          and agents of the Holder, or any controlling person (any person
          referred to in clause (A), (B) or (C) may hereinafter be referred to
          as an "Indemnified Person"), from and against any and all losses,
          claims, damages, liabilities, expenses and judgments caused by any
          untrue statement or alleged untrue statement of a material fact
          contained in any Registration Statement, Prospectus or form of
          Prospectus or in any amendment or supplement thereto or in any
          preliminary Prospectus, or caused by any omission or alleged omission
          to state therein a material fact required to be stated therein or
          necessary to make the statements therein (in the case of any
          Prospectus or form of Prospectus or supplement thereto, in light of
          the circumstances under which they were made) not misleading, except
          insofar as such losses, claims, damages, liabilities, expenses or
          judgments are caused by any such untrue statement or omission or
          alleged untrue statement or omission based upon information relating
          to any Indemnified Person furnished in writing to the Company by or on
          behalf of such Indemnified Person expressly for use therein; provided
          that the foregoing indemnity with respect to any Prospectus shall not
          inure to the benefit of any Indemnified Person from whom the person
          asserting such losses, claims, damages, liabilities, expenses and
          judgments purchased securities if such untrue statement or omission or
          alleged untrue statement or omission made in such Prospectus is
          eliminated or remedied by an amendment or supplement thereto and a
          copy of such amended or supplemented Prospectus shall not have been
          furnished to such person in a timely manner due to the wrongful action
          or wrongful inaction of such Indemnified Person, whether as a result
          of negligence or otherwise.

               (ii) In case any action shall be brought against any Indemnified
          Person, based upon any Registration Statement or any such Prospectus
          or any amendment or supplement thereto and with respect to which
          indemnity may be sought against the Company, such Indemnified Person
          shall promptly notify the Company in writing and the Company shall
          assume the defense thereof, including the employment of counsel
          reasonably satisfactory to such Indemnified Person and payment of all
          reasonable fees


                                      -16-





          and expenses. Any Indemnified Person shall have the right to employ
          separate counsel in any such action, but the fees and expenses of such
          counsel shall be at the expense of such Indemnified Person, unless (A)
          the employment of such counsel shall have been specifically authorized
          in writing by the Company, (B) the Company shall have failed to assume
          the defense and employ counsel or (C) such Indemnified Person or
          Persons shall have been advised by counsel that there may be a
          conflict between the positions of the indemnifying party or parties
          and of the indemnified party or parties in conducting the defense of
          such action or proceeding or that there may be legal defenses
          available to such Indemnified Person or Persons different from or in
          addition to those available to the indemnifying party or parties (in
          which case the Company shall not have the right to assume the defense
          of such action on behalf of such Indemnified Person), it being
          understood, however, that the Company shall not, in connection with
          any one such action or separate but substantially similar or related
          actions in the same jurisdiction arising out of the same general
          allegations or circumstances, be liable for the reasonable fees and
          expenses of more than one separate firm of attorneys (in addition to
          any local counsel) for all such Indemnified Persons, which firm shall
          be designated in writing by such Indemnified Persons. The Company
          shall not be liable for any settlement of any such action effected
          without its written consent, but if settled with the written consent
          of the Company, the Company agrees to indemnify and hold harmless any
          Indemnified Person from and against any loss or liability by reason of
          such settlement. No indemnifying party shall, without the prior
          written consent of the Indemnified Person, effect any settlement of
          any pending or threatened proceeding in respect of which any
          Indemnified Person is or could have been a party and indemnity could
          have been sought hereunder by such Indemnified Person, unless such
          settlement includes an unconditional release of such Indemnified
          Person from all liability on claims that are the subject matter of
          such proceeding.

               (iii) In connection with any Registration Statement in which the
          Holder is participating, the Holder agrees, severally and not jointly,
          to indemnify and hold harmless the Company, its directors, its
          officers and any person controlling the Company within the meaning of
          Section 15 of the Securities Act or Section 20 of the Exchange Act, to
          the same extent as the foregoing indemnity from the Company to each
          Indemnified Person but only with reference to information relating to
          such Indemnified Person furnished in writing by or on behalf of such
          Indemnified Person expressly for use in such Registration Statement.
          In case any action shall be brought against the Company, any of its
          directors, any such officer or any person controlling the Company
          based on such Registration Statement and in respect of which indemnity
          may be sought against any Indemnified Person, the Indemnified Person
          shall have the rights and duties given to the Company (except that if
          the Company shall have assumed the defense thereof, such Indemnified
          Person shall not be required to do so, but may employ separate counsel
          therein but the fees and expenses of such counsel shall be at the
          expense of such Indemnified Person), and the Company, its directors,
          any such officers and any person controlling the Company shall have
          the rights and duties given to the Indemnified Person by Section
          10(g)(ii).

               (iv) If the indemnification provided for in this Section 10(g) is
          unavailable to an indemnified party in respect of any losses, claims,
          damages, liabilities, expenses or judgments referred to therein, then
          each indemnifying party, in lieu of indemnifying


                                      -17-





          such Indemnified Person, shall contribute to the amount paid or
          payable by such Indemnified Person as a result of such losses, claims,
          damages, liabilities, expenses and judgments in such proportion as is
          appropriate to reflect the relative fault of the Company and each such
          Indemnified Person in connection with the statements or omissions
          which resulted in such losses, claims, damages, liabilities, expenses
          or judgments, as well as any other relevant equitable considerations.
          The relative fault of the Company and each such Indemnified Person
          shall be determined by reference to, among other things, whether the
          untrue or alleged untrue statement of a material fact or the omission
          to state a material fact relates to information supplied by the
          Company or such Indemnified Person and the parties' relative intent,
          knowledge, access to information and opportunity to correct or prevent
          such statement or omission.

               The Company and the Holder agree that it would not be just and
          equitable if contribution pursuant to this Section 10(g)(iv) were
          determined by pro rata allocation (even if the Indemnified Person were
          treated as one entity for such purpose) or by any other method of
          allocation which does not take account of the equitable considerations
          referred to in the immediately preceding paragraph. The amount paid or
          payable by an Indemnified Person as a result of the losses, claims,
          damages, liabilities, expenses or judgments referred to in the
          immediately preceding paragraph shall be deemed to include, subject to
          the limitations set forth above, any legal or other expenses
          reasonably incurred by such indemnified party in connection with
          investigating or defending any such action or claim. No person guilty
          of fraudulent misrepresentation (within the meaning of Section 11(f)
          of the Securities Act) shall be entitled to contribution from any
          person who was not guilty of such fraudulent misrepresentation.

          (h) Information by Holder. The Holder shall furnish to the Company
such information regarding such Holder and any distribution proposed by the
Holder as the Company may request in writing or as shall be required in
connection with any registration, qualification or compliance referred to in
this Agreement.

          (i) Rule 144 Reporting. With a view to making available to the Holder
the benefits of certain rules and regulations of the Commission which may permit
the sale of the Shares, Conversion Shares and the Registrable Securities to the
public without registration, the Company agrees to use commercially reasonable
efforts to (a) make and keep public information available, as those terms are
understood and defined in the Commission's Rule 144, at all times, and (b) file
with the Commission in a timely manner all reports and other documents required
of the Company under the Exchange Act.

         11. Notices. All notices and other communication required or
appropriate to be given hereunder shall be in writing and shall be delivered by
hand or mailed by certified mail, return receipt requested, or sent by telex or
facsimile (in which case a confirming copy shall also be sent by certified mail
or courier), to the following respective addresses or to such other addresses as
may be specified in any notice delivered or mailed as above provided:



                                      -18-





                  (a)      If to the Purchaser, to:

                           Genentech, Inc.
                           460 Point San Bruno Boulevard
                           South San Francisco, CA 94080
                           Telephone:       (415) 225-1000
                           Facsimile:       (415) 952-9881

                           Attention:  Corporate Secretary

                  (b)      If to the Company to:

                           Xoma Corporation
                           2910 7th Street
                           Berkeley, CA 94080
                           Telephone:       (510) 644-1170
                           Facsimile:       (510) 649-7571

                           Attention:  General Counsel

Any notice or other communication delivered by hand or mailed shall be deemed to
have been delivered on the date on which such notice or communication is
delivered by hand, or in the case of certified mail deposited with the
appropriate postal authorities on the date when such notice or communication is
actually received, and in any other case shall be deemed to have been delivered
on the date on which such notice or communication is actually received.

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

          13. Amendments. No provision of this Agreement may be waived, changed
or modified, or the discharge thereof acknowledged orally, but only by an
agreement in writing signed by the party against which the enforcement of any
waiver, change, modification or discharge is sought.

          14. Assignment.

               (a) Except as set forth in this Section 14, none of the rights or
          obligations of either party hereto may be assigned or transferred
          without the prior written consent of the other party hereto, provided
          that the rights of the Purchaser and the obligations of the Company
          under Section 10 hereof may be transferred to an Affiliate, to Roche
          or to any bona fide purchaser for value of at least 500,000 shares of
          Registrable Securities, which transfer shall otherwise be in
          compliance with this Agreement, without the prior written consent of
          the Company.

               (b) Neither party may assign any of its rights and obligations
          under this Agreement in connection with a merger or similar
          reorganization or the sale of all or substantially all of its assets;
          provided, however, that the Purchaser may assign such rights and
          obligations under this Agreement to Roche (so long as Roche continues
          to own at least a majority of the outstanding Voting Stock of the
          Purchaser).


                                      -19-






               (c) This Agreement shall be binding upon and inure to the benefit
          of the successors and permitted assigns of the parties. Any assignment
          not in accordance with this Agreement shall be void.

          15. Counterparts. This Agreement 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.

          16. Entire Agreement. This Agreement, the Collaboration Agreement and
the Convertible Note, together with the Exhibits, Schedules and other documents
attached thereto, constitute the entire contract between the parties with
respect to the subject matter hereof and thereof, and no party will be liable or
bound to the other in any manner by any representations, warranties or covenants
except as specifically set forth herein and therein.

          17. Term and Termination. This Agreement is effective as of the date
first written above and, except as otherwise expressly provided herein, will
continue in effect until the later of the date neither the Purchaser nor any of
its Affiliates owns any of the Securities and termination of the Collaboration
Agreement, unless earlier terminated by mutual written consent of both parties.

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

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



                                      -20-




          IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed as of the date first above written.


"COMPANY"                              XOMA CORPORATION




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


"PURCHASER"                            GENENTECH, INC.




                                       By:
                                           ----------------------------------
                                             John P. McLaughlin
                                             Executive Vice President






                                      -21-