THIRD AMENDED AND RESTATED
                          CERTIFICATE OF INCORPORATION
                                       OF
                                   TANOX, INC.
 
      TANOX, INC., a corporation organized and existing under the laws of the
State of Delaware, hereby certifies as follows:
 
      1. The name of the corporation is Tanox, Inc. The date of filing of its
original Certificate of Incorporation with the Secretary of State was the 23rd
day of December 1999. The date of filing of its Amended and Restated Certificate
of Incorporation with the Secretary of State was the 28th day of December 1999.
The date of filing of its Second Amended and Restated Certificate of
Incorporation was the 1st day of February, 2000.
 
      2. This Third Amended and Restated Certificate of Incorporation restates,
integrates and also further amends the certificate of incorporation, as provided
herein.
 
      3. This Third Amended and Restated Certificate of Incorporation was duly
adopted by the affirmative vote of a majority of its stockholders in accordance
with Sections 242 and 245 of the Delaware General Corporation Law.
 
                                   ARTICLE ONE
 
      The name of the corporation is Tanox, Inc.
 
                                   ARTICLE TWO
 
      The address of the Corporation's registered office in the State of
Delaware is Corporation Trust Center, 1209 Orange Street, New Castle County,
Wilmington, Delaware 19801. The name of its registered agent at such address is
The Corporation Trust Company.
 
                                  ARTICLE THREE
 
      The purpose of the Corporation is to engage in any lawful act or activity
for which corporations may be organized under the General Corporation Law of the
State of Delaware (the "DGCL").
 
                                  ARTICLE FOUR
 
      The total number of shares of all classes of stock which the Corporation
shall have authority to issue is 130,000,000 shares which shall be divided into
(a) 10,000,000
 
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shares, designated as Preferred Stock, having a par value of $.01 per share (the
"Preferred Stock"), and (b) 120,000,000 shares, designated as Common Stock,
having a par value of $.01 per share (the "Common Stock").
 
      A statement of the powers, preferences and rights, and the qualifications,
limitations or restrictions thereof, in respect of each class of stock of the
Corporation is as follows:
 
A.    PREFERRED STOCK
 
      The Preferred Stock may be issued from time to time by the Board of
Directors as shares of one or more classes or series. Subject to the provisions
of this Certificate of Incorporation and the limitations prescribed by law, the
Board of Directors is expressly authorized by adopting resolutions to issue the
shares, fix the number of shares and change the number of shares constituting
any series, and to provide for or change the voting powers, designations,
preferences and relative, participating, optional or other special rights,
qualifications, limitations or restrictions thereof, including dividend rights
(and whether dividends are cumulative), dividend rates, terms of redemption
(including sinking fund provisions), a redemption price or prices, conversion
rights and liquidation preferences of the shares constituting any class or
series of the Preferred Stock, without any further action or vote by the
stockholders.
 
B.    COMMON STOCK
 
      1.    DIVIDENDS.
 
      Subject to the preferred rights of the holders of shares of any class or
series of Preferred Stock as provided by the Board of Directors with respect to
any such class or series of Preferred Stock, the holders of the Common Stock
shall be entitled to receive, as and when declared by the Board of Directors out
of the funds of the Corporation legally available therefor, such dividends of
the funds of the Corporation legally available therefor, such dividends (payable
in cash, stock or otherwise) as the Board of Directors may from time to time
determine, payable to stockholders of record on such dates, not exceeding 60
days preceding the dividend payment dates, as shall be fixed for such purpose by
the Board of Directors in advance of payment of each particular dividend.
 
      2.    LIQUIDATION.
 
      In the event of any liquidation, dissolution or winding up of the
Corporation, whether voluntary or involuntary, after the distribution or payment
to the holders of shares of any class or series of Preferred Stock as provided
by the Board of Directors with respect to any such class or series of Preferred
Stock, the remaining assets of the Corporation available for distribution to
stockholders shall be distributed among and paid to the holders of Common Stock
ratably in proportion to the number of shares of Common Stock held by them
respectively.
 
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      3.    VOTING RIGHTS.
 
      Except as otherwise required by law, each holder of shares of Common Stock
shall be entitled to one vote for each share of Common Stock standing in such
holder's name on the books of the Corporation.
 
                                  ARTICLE FIVE
 
A.    BOARD OF DIRECTORS.
 
      The number of directors shall be fixed from time to time exclusively by
the Board of Directors pursuant to a resolution adopted by a majority of the
directors then in office.
 
      Except as otherwise provided in the initial Bylaws of the Corporation, at
each annual meeting of stockholders, the successors to the directors whose term
expires at that meeting shall be elected to hold office for a term expiring at
the annual meeting of stockholders held in the year following the year of their
election and until their successors have been duly elected and qualified. At
each annual meeting of stockholders at which a quorum is present, the persons
receiving a plurality of the votes cast shall be directors. No director may be
removed from office by a vote of the stockholders at any time except for cause.
Election of directors need not be by written ballot unless the Bylaws of the
Corporation so provide.
 
B.    VACANCIES.
 
      Any vacancy on the Board of Directors resulting from death, retirement,
resignation, disqualification or removal from office or other cause, as well as
any vacancy resulting from an increase in the number of directors which occurs
between annual meetings of the stockholders at which directors are elected,
shall be filled only by a majority vote of the remaining directors then in
office, though less than a quorum, except that those vacancies resulting from
removal from office by a vote of the stockholders may be filled by a vote of the
stockholders at the same meeting at which such removal occurs. The directors
chosen to fill vacancies shall hold office for a term expiring at the end of the
next annual meeting of stockholders at which the term to which they have been
elected expires. No decrease in the number of directors constituting the Board
of Directors shall shorten the term of any incumbent director.
 
      Notwithstanding the foregoing, whenever the holders of one or more classes
or series of Preferred Stock shall have the right, voting separately, as a class
or series, to elect directors, the election, term of office, filling of
vacancies, removal and other features of such directorships shall be governed by
the terms of the resolution or resolutions adopted by the Board of Directors
pursuant to ARTICLE FOUR applicable thereto, and each director so elected shall
not be subject to the provisions of this ARTICLE FIVE unless otherwise provided
therein.
 
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C.    POWER TO MAKE, ALTER AND REPEAL BYLAWS.
 
      In furtherance and not in limitation of the powers conferred by statute,
the Board of Directors is expressly authorized to adopt, amend and repeal the
Bylaws of the Corporation subject to the power of the stockholders of the
Corporation to adopt, amend and repeal any Bylaw whether adopted by them or
otherwise.
 
                                   ARTICLE SIX
 
      The Corporation reserves the right to amend, alter, change or repeal any
provision in this Certificate of Incorporation, in the manner now or hereafter
prescribed by statute.
 
                                  ARTICLE SEVEN
 
      No director of the Corporation shall be liable to the Corporation or its
stockholders for monetary damages for breach of fiduciary duty as a director,
except for liability (i) for any breach of the director's duty of loyalty to the
Corporation or its stockholders, (ii) for acts or omissions not in good faith or
which involve intentional misconduct or a knowing violation of law, (iii) under
Section 174 of the DGCL or (iv) for any transaction from which the director
derived an improper personal benefit.
 
                                  ARTICLE EIGHT
 
      The Corporation shall, to the fullest extent permitted by Section 145 of
the DGCL, as the same may be amended and supplemented, indemnify each director
and officer of the Corporation from and against any and all of the expenses,
liabilities or other matters referred to in or covered by such section and the
indemnification provided for herein shall not be deemed exclusive of any other
rights to which those indemnified may be entitled under any Bylaw, agreement,
vote of stockholders, vote of disinterested directors or otherwise, and shall
continue as to a person who has ceased to be a director or officer and shall
inure to the benefit of the heirs, executors and administrators of such persons
and the Corporation may purchase and maintain insurance on behalf of any
director or officer to the extent permitted by Section 145 of the DGCL.
 
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                                  ARTICLE NINE
 
      Special Meetings of the Corporation's stockholders may be called by the
President, the Board of Directors, or such other person or persons as may be
authorized in the Bylaws.
 
                                   ARTICLE TEN
 
      Any action required or permitted to be taken by the stockholders of the
Corporation at an annual or special meeting of stockholders must be effected at
a duly called meeting and may not be taken or effected by a written consent of
stockholders in lieu thereof.
 
      IN WITNESS WHEREOF, Tanox, Inc. has caused this Third Amended and Restated
Certificate of Incorporation to be signed by John Blickenstaff, its Vice
President of Administration, Secretary and Treasurer this ___ day of
_______________, 2000 to be effective as of the ___ day of ______________, 2000.
 
 
 
                                         TANOX, INC.
 
 
                                         _______________________________________
                                         John Blickenstaff, Vice President of
                                         Administration, Secretary and Treasurer