IGEN INTERNATIONAL INC.
                                  EXHIBIT 3.1

                         CERTIFICATE OF INCORPORATION

                                      OF

                           IGEN INTERNATIONAL, INC.


     The undersigned, a natural person (the "Sole Incorporator"), for the
purpose of organizing a corporation to conduct the business and promote the
purposes hereinafter stated, under the provisions and subject to the
requirements of the laws of the State of Delaware hereby certifies that:

                                      I.

     The name of this corporation is IGEN International, Inc.

                                      II.

     The address of the registered office of the corporation in the State of
Delaware is 1013 Centre Road, City of Wilmington, County of New Castle, and the
name of the registered agent of the corporation in the State of Delaware at such
address is The Prentice-Hall Corporation System, Inc.

                                     III.

     The purpose of this corporation is to engage in any lawful act or activity
for which a corporation may be organized under the General Corporation Law of
the State of Delaware.

                                      IV.

     A.   This corporation is authorized to issue two classes of stock to be
designated, respectively, "Common Stock" and "Preferred Stock."  The total
number of shares which the corporation is authorized to issue is Sixty Million
(60,000,000) shares.  Fifty Million (50,000,000) shares shall be Common Stock,
each having a par value of one-tenth of one cent ($.001).  Ten Million
(10,000,000) shares shall be Preferred Stock, each having a par value of one-
tenth of one cent ($.001).

     B.   The Preferred Stock may be issued from time to time in one or more
series.  The Board of Directors is hereby authorized, by filing a certificate (a
"Preferred Stock Designation") pursuant to the Delaware General Corporation Law,
to fix or alter from time to time the designation, powers, preferences and
rights of the shares of each such series and the qualifications, limitations or
restrictions of any wholly unissued series of Preferred Stock, and to 

                                      1.

 
establish from time to time the number of shares constituting any such series or
any of them; and to increase or decrease the number of shares of any series
subsequent to the issuance of shares of that series, but not below the number of
shares of such series then outstanding. In case the number of shares of any
series shall be decreased in accordance with the foregoing sentence, the shares
constituting such decrease shall resume the status that they had prior to the
adoption of the resolution originally fixing the number of shares of such
series.

     C.   Six Hundred Thousand (600,000) shares of Preferred Stock, $.001 par
value, are hereby designated "Series A Junior Participating Preferred Stock"
with the rights, preferences, privileges and restrictions specified herein (the
"Junior Preferred Stock").  Such number of shares may be increased or decreased
by resolution of the Board of Directors; provided, that no decrease shall reduce
the number of shares of Junior Preferred Stock to a number less than the number
of shares then outstanding plus the number of shares reserved for issuance upon
the exercise of outstanding options, rights or warrants or upon the conversion
of any outstanding securities issued by the corporation convertible into Junior
Preferred Stock.

          (1)  Dividends and Distributions.

               (a)  Subject to the rights of the holders of any shares of any
series of Preferred Stock (or any similar stock) ranking prior and superior to
the Junior Preferred Stock with respect to dividends, the holders of shares of
Junior Preferred Stock, in preference to the holders of Common Stock, par value
$.001 per share (the "Common Stock"), of the corporation, and of any other
junior stock, shall be entitled to receive, when, as and if declared by the
Board of Directors out of funds legally available for the purpose, quarterly
dividends payable in cash on the first day of March, June, September and
December in each year (each such date being referred to herein as a "Quarterly
Dividend Payment Date"), commencing on the first Quarterly Dividend Payment Date
after the first issuance of a share or fraction of a share of Junior Preferred
Stock, in an amount per share (rounded to the nearest cent) equal to the greater
of (a) $l.00 or (b) subject to the provision for adjustment hereinafter set
forth, 100 times the aggregate per share amount of all cash dividends, and 100
times the aggregate per share amount (payable in kind) of all non-cash dividends
or other distributions, other than a dividend payable in shares of Common Stock
or a subdivision of the outstanding shares of Common Stock (by reclassification
or otherwise) declared on the Common Stock since the immediately preceding
Quarterly Dividend Payment Date or, with respect to the first Quarterly Dividend
Payment Date, since the first issuance of any share or fraction of a share of
Junior Preferred Stock. In the event the corporation shall at any time declare
or pay any dividend on the Common Stock payable in shares of Common Stock, or
effect a subdivision or combination or consolidation of the outstanding shares
of Common Stock (by reclassification or otherwise than by payment of a dividend
in shares of Common Stock) into a greater or lesser number of shares of Common
Stock, then in each such case the amount to which holders of shares of Junior
Preferred Stock were entitled immediately prior to such event under clause (b)
of the preceding sentence shall be adjusted by multiplying such amount by a
fraction, the numerator of which is the number of shares of 

                                      2.

 
Common Stock outstanding immediately after such event and the denominator of
which is the number of shares of Common Stock that were outstanding immediately
prior to such event.

               (b)  The corporation shall declare a dividend or distribution on
the Junior Preferred Stock as provided in paragraph (A) of this Section
immediately after it declares a dividend or distribution on the Common Stock
(other than a dividend payable in shares of Common Stock); provided that, in the
event no dividend or distribution shall have been declared on the Common Stock
during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $1.00 per share on the
Junior Preferred Stock shall nevertheless be payable on such subsequent
Quarterly Dividend Payment Date.

               (c)  Dividends shall begin to accrue and be cumulative on
outstanding shares of Junior Preferred Stock from the Quarterly Dividend Payment
Date next preceding the date of issue of such shares, unless the date of issue
of such shares is prior to the record date for the first Quarterly Dividend
Payment Date, in which case dividends on such shares shall begin to accrue from
the date of issue of such shares, or unless the date of issue is a Quarterly
Dividend Payment Date or is a date after the record date for the determination
of holders of shares of Junior Preferred Stock entitled to receive a quarterly
dividend and before such Quarterly Dividend Payment Date, in either of which
events such dividends shall begin to accrue and be cumulative from such
Quarterly Dividend Payment Date. Accrued but unpaid dividends shall not bear
interest. Dividends paid on the shares of Junior Preferred Stock in an amount
less than the total amount of such dividends at the time accrued and payable on
such shares shall be allocated pro rata on a share-by-share basis among all such
shares at the time outstanding. The Board of Directors may fix a record date for
the determination of holders of shares of Junior Preferred Stock entitled to
receive payment of a dividend or distribution declared thereon, which record
date shall be not more than 60 days prior to the date fixed for the payment
thereof.

          (2)  Voting Rights.  The holders of shares of Junior Preferred Stock
shall have the following voting rights:

               (a)  Subject to the provision for adjustment hereinafter set
forth, each share of Junior Preferred Stock shall entitle the holder thereof to
100 votes on all matters submitted to a vote of the shareholders of the
corporation. In the event the corporation shall at any time declare or pay any
dividend on the Common Stock payable in shares of Common Stock, or effect a
subdivision or combination or consolidation of the outstanding shares of Common
Stock (by reclassification or otherwise than by payment of a dividend in shares
of Common Stock) into a greater or lesser number of shares of Common Stock, then
in each such case the number of votes per share to which holders of shares of
Junior Preferred Stock were entitled immediately prior to such event shall be
adjusted by multiplying such number by a fraction, the numerator of which is the
number of shares of Common Stock outstanding immediately after such event and
the denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

                                      3.

 
               (b)  Except as otherwise provided herein, in any other
Certificate of Determination of Preferences creating a series of Preferred Stock
or any similar stock, or by law, the holders of shares of Junior Preferred Stock
and the holders of shares of Common Stock and any other capital stock of the
corporation having general voting rights shall vote together as one class on all
matters submitted to a vote of shareholders of the corporation.

               (c)  Except as set forth herein, or as otherwise provided by law,
holders of Junior Preferred Stock shall have no special voting rights and their
consent shall not be required (except to the extent they are entitled to vote
with holders of Common Stock as set forth herein) for taking any corporate
action.

          (3)  Certain Restrictions.

               (a)  Whenever quarterly dividends or other dividends or
distributions payable on the Junior Preferred Stock as provided in Section 2 are
in arrears, thereafter and until all accrued and unpaid dividends and
distributions, whether or not declared, on shares of Junior Preferred Stock
outstanding shall have been paid in full, the corporation shall not:

                    (i)    declare or pay dividends, or make any other
distributions, on any shares of stock ranking junior (either as to dividends or
upon liquidation, dissolution or winding up) to the Junior Preferred Stock;

                    (ii)   declare or pay dividends, or make any other
distributions, on any shares of stock ranking on a parity (either as to
dividends or upon liquidation, dissolution or winding up) with the Junior
Preferred Stock, except dividends paid ratably on the Junior Preferred Stock and
all such parity stock on which dividends are payable or in arrears in proportion
to the total amounts to which the holders of all such shares are then entitled;

                    (iii)  redeem or purchase or otherwise acquire for
consideration shares of any stock ranking junior (either as to dividends or upon
liquidation, dissolution or winding up) to the Junior Preferred Stock, provided
that the corporation may at any time redeem, purchase or otherwise acquire
shares of any such junior stock in exchange for shares of any stock of the
corporation ranking junior (either as to dividends or upon dissolution,
liquidation or winding up) to the Junior Preferred Stock; or

                    (iv)   redeem or purchase or otherwise acquire for
consideration any shares of Junior Preferred Stock, or any shares of stock
ranking on a parity with the Junior Preferred Stock, except in accordance with a
purchase offer made in writing or by publication (as determined by the Board of
Directors) to all holders of such shares upon such terms as the Board of
Directors, after consideration of the respective annual dividend rates and other
relative rights and preferences of the respective series and classes, shall
determine in good faith will result in fair and equitable treatment among the
respective series or classes.

                                      4.

 
               (b)  The corporation shall not permit any subsidiary of the
corporation to purchase or otherwise acquire for consideration any shares of
stock of the corporation unless the corporation could, under paragraph (A) of
this Section 4, purchase or otherwise acquire such shares at such time and in
such manner.

          (4)  Reacquired Shares. Any shares of Junior Preferred Stock purchased
or otherwise acquired by the corporation in any manner whatsoever shall be
retired and cancelled promptly after the acquisition thereof. All such shares
shall upon their cancellation become authorized but unissued shares of Preferred
Stock and may be reissued as part of a new series of Preferred Stock subject to
the conditions and restrictions on issuance set forth herein, in the Amended and
Restated Articles of Incorporation, or in any other Certificate of Determination
of Preferences creating a series of Preferred Stock or any similar stock or as
otherwise required by law.

          (5)  Liquidation, Dissolution or Winding Up.  Upon any liquidation,
dissolution or winding up of the corporation, no distribution shall be made (1)
to the holders of shares of stock ranking junior (either as to dividends or upon
liquidation, dissolution or winding up) to the Junior Preferred Stock unless,
prior thereto, the holders of shares of Junior Preferred Stock shall have
received the greater of: (A) $100 per share, plus an amount equal to accrued and
unpaid dividends and distributions thereon, whether or not declared, to the date
of such payment; or (B) an aggregate amount per share, subject to the provision
for adjustment hereinafter set forth, equal to 100 times the aggregate amount to
be distributed per share to holders of shares of Common Stock, or (2) to the
holders of shares of stock ranking on a parity (either as to dividends or upon
liquidation, dissolution or winding up) with the Junior Preferred Stock, except
distributions made ratably on the Junior Preferred Stock and all such parity
stock in proportion to the total amounts to which the holders of all such shares
are entitled upon such liquidation, dissolution or winding up.  In the event the
corporation shall at any time declare or pay any dividend on the Common Stock
payable in shares of Common Stock, or effect a subdivision or combination or
consolidation of the outstanding shares of Common Stock (by reclassification or
otherwise than by payment of a dividend in shares of Common Stock) into a
greater or lesser number of shares of Common Stock, then in each such case the
aggregate amount to which holders of shares of Junior Preferred Stock were
entitled immediately prior to such event under the proviso in clause (1) of the
preceding sentence shall be adjusted by multiplying such amount by a fraction
the numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

          (6)  Consolidation, Merger, etc. In case the corporation shall enter
into any consolidation, merger, combination or other transaction in which the
shares of Common Stock are exchanged for or changed into other stock or
securities, cash and/or any other property, then in any such case each share of
Junior Preferred Stock shall at the same time be similarly exchanged or changed
into an amount per share, subject to the provision for adjustment 

                                      5.

 
hereinafter set forth, equal to 100 times the aggregate amount of stock,
securities, cash and/or any other property (payable in kind), as the case may
be, into which or for which each share of Common Stock is changed or exchanged.
In the event the corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the amount set forth in the preceding sentence with respect to the
exchange or change of shares of Junior Preferred Stock shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

          (7)  No Redemption.  The shares of Junior Preferred Stock shall not be
redeemable.

          (8)  Rank.  The Junior Preferred Stock shall rank, with respect to the
payment of dividends and the distribution of assets, junior to all other series
of the corporation's Preferred Stock.

          (9)  Amendment. The Certificate of Incorporation of the corporation
shall not be amended in any manner which would materially alter or change the
powers, preferences or special rights of the Junior Preferred Stock so as to
affect them adversely without the affirmative vote of the holders of at least
two-thirds of the outstanding shares of Junior Preferred Stock, voting together
as a single class.

                                      V.

     For the management of the business and for the conduct of the affairs of
the corporation, and in further definition, limitation and regulation of the
powers of the corporation, of its directors and of its stockholders or any class
thereof, as the case may be, it is further provided that:

     A.

          (1)  The management of the business and the conduct of the affairs of
the corporation shall be vested in its Board of Directors. The number of
directors which shall constitute the whole Board of Directors shall be fixed
exclusively by one or more resolutions adopted by the Board of Directors.

          (2)  Subject to the rights of the holders of any series of Preferred
Stock to elect additional directors under specified circumstances, the directors
shall be divided into three classes designated as Class I, Class II and Class
III, respectively. Directors shall be assigned to each 

                                      6.

 
class in accordance with a resolution or resolutions adopted by the Board of
Directors. At the first annual meeting of stockholders following the adoption
and filing of this Certificate of Incorporation, the term of office of the Class
I directors shall expire and Class I directors shall be elected for a full term
of three years. At the second annual meeting of stockholders following the
adoption and filing of this Certificate of Incorporation, the term of office of
the Class II directors shall expire and Class II directors shall be elected for
a full term of three years. At the third annual meeting of stockholders
following the adoption and filing of this Certificate of Incorporation, the term
of office of the Class III directors shall expire and Class III directors shall
be elected for a full term of three years. At each succeeding annual meeting of
stockholders, directors shall be elected for a full term of three years to
succeed the directors of the class whose terms expire at such annual meeting.

     Notwithstanding the foregoing provisions of this Article, each director
shall serve until his or her successor is duly elected and qualified or until
his or her death, resignation or removal.  No decrease in the number of
directors constituting the Board of Directors shall shorten the term of any
incumbent director.

          (3)  Subject to the rights of the holders of any series of Preferred
Stock, no director shall be removed without cause. Subject to any limitations
imposed by law, the Board of Directors or any individual director may be removed
from office at any time with cause by the affirmative vote of the holders of a
majority of the voting power of all the then-outstanding shares of voting stock
of the corporation, entitled to vote at an election of directors (the "Voting
Stock").

          (4)  Subject to the rights of the holders of any series of Preferred
Stock, any vacancies on the Board of Directors resulting from death,
resignation, disqualification, removal or other causes and any newly created
directorships resulting from any increase in the number of directors, shall,
unless the Board of Directors determines by resolution that any such vacancies
or newly created directorships shall be filled by the stockholders, except as
otherwise provided by law, be filled only by the affirmative vote of a majority
of the directors then in office, even though less than a quorum of the Board of
Directors, and not by the stockholders. Any director elected in accordance with
the preceding sentence shall hold office for the remainder of the full term of
the director for which the vacancy was created or occurred and until such
director's successor shall have been elected and qualified.

     B.

          (1)  Subject to paragraph (g) of Section 43 of the Bylaws, the Bylaws
may be altered or amended or new Bylaws adopted by the affirmative vote of at
least sixty-six and two-thirds percent (66-2/3%) of the voting power of all of
the then-outstanding shares of the Voting Stock. The Board of Directors shall
also have the power to adopt, amend, or repeal Bylaws.

                                      7.

 
          (2)  The directors of the corporation need not be elected by written
ballot unless the Bylaws so provide.

          (3)  No action shall be taken by the stockholders of the corporation
except at an annual or special meeting of stockholders called in accordance with
the Bylaws. No action shall be taken by the stockholders by written consent.

          (4)  Special meetings of the stockholders of the corporation may be
called, for any purpose or purposes, by (i) the Chairman of the Board of
Directors, (ii) the Chief Executive Officer, or (iii) the Board of Directors
pursuant to a resolution adopted by a majority of the total number of authorized
directors (whether or not there exist any vacancies in previously authorized
directorships at the time any such resolution is presented to the Board of
Directors for adoption), and shall be held at such place, on such date, and at
such time as the Board of Directors shall fix.

          (5)  Advance notice of stockholder nominations for the election of
directors and of business to be brought by stockholders before any meeting of
the stockholders of the corporation shall be given in the manner provided in the
Bylaws of the corporation.

                                      VI.

     A.   A director of the corporation shall not be personally liable to the
corporation or its stockholders for monetary damages for any 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 Delaware General Corporation
Law, or (iv) for any transaction from which the director derived an improper
personal benefit.  If the Delaware General Corporation Law is amended after
approval by the stockholders of this Article to authorize corporate action
further eliminating or limiting the personal liability of directors, then the
liability of a director shall be eliminated or limited to the fullest extent
permitted by the Delaware General corporation Law, as so amended.

     B.   Any repeal or modification of this Article VI shall be prospective and
shall not affect the rights under this Article VI in effect at the time of the
alleged occurrence of any act or omission to act giving rise to liability or
indemnification.

                                     VII.

     A.   The corporation reserves the right to amend, alter, change or repeal
any provision contained in this Certificate of Incorporation, in the manner now
or hereafter prescribed by statute, except as provided in paragraph B. of this
Article VII, and all rights conferred upon the stockholders herein are granted
subject to this reservation.

                                      8.

 
     B.   Notwithstanding any other provisions of this Certificate of
Incorporation or any provision of law which might otherwise permit a lesser vote
or no vote, but in addition to any affirmative vote of the holders of any
particular class or series of the Voting Stock required by law, this Certificate
of Incorporation or any Preferred Stock Designation, the affirmative vote of the
holders of at least sixty-six and two-thirds percent (66-2/3%) of the voting
power of all of the then-outstanding shares of the Voting Stock, voting together
as a single class, shall be required to alter, amend or repeal Articles V, VI,
and VII.

                                     VIII.

     The name and the mailing address of the Sole Incorporator is as follows:

          Name                      Mailing Address

          Andrei M. Manoliu         Cooley Godward Castro
                                    Huddleson & Tatum
                                    3000 El Camino Real
                                    5 Palo Alto Square
                                    4th Floor
                                    Palo Alto, CA 94306-2155

     In Witness Whereof, this Certificate has been subscribed this 29th day of
August, 1996 by the undersigned who affirms that the statements made herein
are true and correct.


                                    /s/ Andrei M. Manoliu
                                    ------------------------------------------
                                    Andrei M. Manoliu
                                    Sole Incorporator

                                      9.