FORM OF VOTING AGREEMENT

Exhibit 10.1

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FORM OF VOTING AGREEMENT

THIS VOTING AGREEMENT (this “ Agreement ”) is made and entered into as of November 9, 2006, by and between Genentech, Inc., a Delaware corporation (“ Parent ”) and the undersigned stockholder (“ Stockholder ”) of Tanox, Inc. (the “ Company ”).

RECITALS

A. Concurrently with the execution of this Agreement, Parent and the Company have entered into an Agreement and Plan of Merger (the “ Merger Agreement ”), which provides for the merger (the “ Merger ”) of a wholly-owned subsidiary of Parent with and into the Company.

B. Pursuant to the Merger, all of the issued and outstanding shares of capital stock and options of the Company will be canceled and converted into the right to receive the consideration set forth in the Merger Agreement, all upon the terms and subject to the conditions set forth in the Merger Agreement.

C. As of the date hereof, Stockholder is the beneficial owner (as defined in Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”)) of the number of shares of outstanding capital stock of the Company (the “ Shares ”) and other securities convertible into, or exercisable or exchangeable for, shares of capital stock of the Company (the “ Options ”), all as set forth on the signature page of this Agreement; provided that for purposes of determining beneficial ownership pursuant to this Agreement, Stockholder shall in all cases be deemed to be the beneficial owner of any securities which may be acquired by such Stockholder pursuant to any agreement, arrangement or understanding or upon the exercise of conversion rights, exchange rights, warrants or options, or otherwise (irrespective of whether the right to acquire such securities is exercisable immediately or only after the passage of time, including the passage of time in excess of 60 days, the satisfaction of any conditions, the occurrence of any event or any combination of the foregoing).

D. As a material inducement to Parent to enter into and to consummate the transactions contemplated by the Merger Agreement, Parent has required that Stockholder agree, and Stockholder is willing to agree, to restrict the transfer or disposition of any Shares, Options and any New Shares (as defined in Section 1(b) hereof), and to vote the Shares and any New Shares as set forth in this Agreement.

NOW, THEREFORE, the parties hereto hereby agree as follows:

1. Agreement to Retain Shares and Options .

(a) Transfer . Stockholder agrees that, at all times during the period beginning on the date hereof and ending at the Expiration Time, Stockholder shall not Transfer (as defined below) any of the Shares, Options and any New Shares, or make any agreement or understanding

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regarding any Transfer, in each case without the prior written consent of Parent. Stockholder agrees that any Transfer in violation of this Agreement shall be void and of no force or effect.

As used herein, the term “ Expiration Time ” shall mean the earlier to occur of (i) such date and time as the Merger shall become effective in accordance with the terms and provisions of the Merger Agreement, or (ii) the termination of the Merger Agreement in accordance with the terms thereof. As used herein, the term “ Transfer ” shall mean, with respect to any security, the direct or indirect assignment, sale, transfer, tender, pledge, hypothecation, or the gift, placement in trust, or the Constructive Sale (as defined below) or other disposition of such security (excluding [exercises of Options and] ¹ transfers by testamentary or intestate succession or otherwise by operation of law) or any right, title or interest therein (including, but not limited to, any right or power to vote to which the holder thereof may be entitled, whether such right or power is granted by proxy or otherwise), or the record or beneficial ownership thereof, the offer to make such a sale, transfer, tender, pledge, hypothecation or Constructive Sale or other disposition, and each agreement, arrangement or understanding, whether or not in writing, to effect any of the foregoing, excluding any Transfer (A) pursuant to a court order, (B) pursuant to the Merger, (C) to any affiliate or family member of Stockholder if such transferee, prior to the Transfer, executes a binding agreement with Parent and the Company substantially in the form of this Agreement [or (D) that is a sale (other than a Constructive Sale) in the open market through a brokers’ transaction (as defined in Rule 144(g) under the Securities Act of 1933, as amended)] ² . As used herein, the term “ Constructive Sale ” shall mean, with respect to any security, a short sale with respect to such security, entering into or acquiring an offsetting derivative contract with respect to such security, entering into or acquiring a futures or forward contract to deliver such security or entering into any other hedging or other derivative transaction that has the effect of materially changing the economic benefits and risks of ownership.

(b) New Shares . Stockholder agrees that any shares of capital stock of the Company that Stockholder purchases or with respect to which Stockholder otherwise acquires beneficial ownership after the date of this Agreement and prior to the Expiration Time, including, without limitation, shares issued or issuable upon the conversion, exercise or exchange, as the case may be, of any Options held by Stockholder (“ New Shares ”), shall be subject to the terms and conditions of this Agreement to the same extent as if they constituted Shares as of the date hereof.

2. Agreement to Vote Shares . Until the Expiration Time, at every meeting of stockholders of the Company called with respect to any of the following, and at every adjournment or postponement thereof, and on every action or approval by written consent of stockholders of the Company with respect to any of the following, Stockholder shall vote, to the extent not voted by the person(s) appointed under the Proxy (as defined in Section 3 ), the outstanding Shares and any outstanding New Shares (to the extent any such New Shares may be voted):

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(i) in favor of adoption of the Merger Agreement and in favor of any other action contemplated by the Merger Agreement or required in furtherance of the Merger and the transactions contemplated by the Merger Agreement (including one or more adjournments necessary to solicit additional proxies if there are insufficient votes to adopt the Merger Agreement and any such related proposals at the time of any meeting held for such purposes);

(ii) against approval of any proposal made in opposition to, or in competition with, consummation of the Merger and the transactions contemplated by the Merger Agreement;

(iii) against any of the following actions (other than those actions contemplated by the Merger Agreement): (A) any merger, consolidation, business combination, sale of assets, reorganization or recapitalization of the Company or any subsidiary of the Company with any party, (B) any sale, lease, license or transfer of any significant part of the assets of the Company or any subsidiary of the Company, (C) any reorganization, recapitalization, dissolution, liquidation or winding up of the Company or any subsidiary of the Company, (D) any amendment to the certificate of incorporation or bylaws of the Company or any subsidiary of the Company or any material change in the capitalization of the Company or any subsidiary of the Company, or the corporate structure of the Company or any subsidiary of the Company, or (E) any other action that is intended, or could reasonably be expected to, impede, frustrate, prevent, interfere with, delay, postpone, discourage, nullify or adversely affect the Merger, the Merger Agreement or any of the other transactions contemplated by the Merger Agreement; and

(iv) in favor of waiving any notice that may have been or may be required relating to any such meeting of stockholders or written consent, the Merger, the Merger Agreement or the transactions contemplated thereby.

Prior to the Expiration Time, Stockholder shall not enter into any agreement or understanding with any person to vote or give instructions in any manner inconsistent with this Section 2 . Prior to the Expiration Time, to the extent not represented thereat by the person(s) appointed under the Proxy, Stockholder shall [cause the Shares and any New Shares to be counted as present thereat for purposes of establishing quorum.] ³

3. Irrevocable Proxy . Concurrently with the execution of this Agreement, Stockholder agrees to deliver to Parent an irrevocable proxy in the form attached hereto as Appendix A (the “ Proxy ”), which shall be irrevocable to the fullest extent permitted by applicable law, covering the total number of Shares and New Shares.

4. Representations, Warranties and Covenants of Stockholder . Stockholder represents, warrants and covenants to Parent as follows:

(i) Stockholder is the beneficial owner of the Shares, with full power to vote or direct the voting of the Shares and to dispose of the Shares for and on behalf of any and all beneficial owners of the Shares, with no limitations, qualifications or restrictions on such rights.

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(ii) As of the date hereof, the Shares are, and at all times up until the Expiration Time the Shares will be, free and clear of any rights of first refusal, co-sale rights, security interests, liens, pledges, claims, options, charges or other encumbrances of any kind or nature, in each case that could impair Stockholder’s ability to fulfill its obligations under Section 2 . The execution and delivery of this Agreement by Stockholder do not, and Stockholder’s performance of its obligations under this Agre