Document:

Exhibit 10.1

                               PURCHASE AGREEMENT

         This PURCHASE AGREEMENT (this "Agreement"), dated as of March 8, 2002,
is entered into by and between IGEN International, Inc., a Delaware corporation
(the "Company"), and Acqua Wellington Private Placement Fund, Ltd., a company
organized under the laws of the Commonwealth of the Bahamas (the "Purchaser"),
for the purchase and sale of shares of the common stock, par value $.001 per
share (the "Common Stock"), of the Company by the Purchaser, in the manner, and
upon the terms, provisions and conditions set forth in this Agreement.

         WHEREAS, the parties desire that, upon the terms and subject to the
conditions contained herein, the Company shall issue and sell to the Purchaser
and Purchaser shall purchase shares of Common Stock; and

         WHEREAS, such purchase and sale will be made in reliance upon the
provisions of Section 4(2) and Rule 506 of Regulation D ("Regulation D") of the
United States Securities Act of 1933, as amended, and regulations promulgated
thereunder (the "Securities Act"), or upon such other exemption from the
registration requirements of the Securities Act as may be available with respect
to any or all of the purchases of Common Stock to be made hereunder.

         NOW, THEREFORE, in consideration of the representations, warranties and
agreements contained herein and other good and valuable consideration, the
receipt and legal adequacy of which is hereby acknowledged by the parties, the
Company and the Purchaser hereby agree as follows:

         1.       Purchase Price.
                  (a) Upon the following terms and subject to the conditions
contained herein, the Purchaser hereby agrees to purchase 560,000 shares of the
Company's Common Stock (the "Shares") at a per share price of $36.8094 ("Per
Share Purchase Price") and for an aggregate purchase price of $20,613,287 (the
"Purchase Price").

                  (b) The Company has authorized and has reserved and covenants
to continue to reserve, free of preemptive rights and other similar contractual
rights of stockholders, a sufficient number of its authorized but unissued
shares of Common Stock, to effect the issuance of the Shares.

                  (c) In consideration of and in express reliance upon the
representations, warranties, covenants, terms and conditions of this Agreement,
the Company agrees to issue and sell to the Purchaser and the Purchaser agrees
to purchase the Shares. The closing under this Agreement (the "Closing") shall
take place at the offices of Jenkens & Gilchrist Parker Chapin LLP, The Chrysler
Building, 405 Lexington Avenue, New York, New York 10174 at 1:00 p.m. on March
11, 2002 (eastern time)

<PAGE>

upon the satisfaction of each of the conditions set forth in Sections 4 and 5
hereof (the "Closing Date").

         2.       Representations,  Warranties  and Covenants of the Purchaser.
The Purchaser represents and warrants to the Company, and covenants for the
benefit of the Company, as follows:

                  (a) The Purchaser is a limited liability company duly
organized, validly existing and in good standing under the laws of the
Commonwealth of The Bahamas.

                  (b) This Agreement has been duly authorized, validly executed
and delivered by the Purchaser and is a valid and binding agreement and
obligation of the Purchaser enforceable against the Purchaser in accordance with
its terms, subject to limitations on enforcement by general principles of equity
and by bankruptcy or other laws affecting the enforcement of creditors' rights
generally, and the Purchaser has full power and authority to execute and deliver
this Agreement and the other agreements and documents contemplated hereby and to
perform its obligations hereunder and thereunder.

                  (c) The Purchaser has received and carefully reviewed copies
of the Public Documents (as hereinafter defined). The Purchaser understands that
no Federal, state, local or foreign governmental body or regulatory authority
has made any finding or determination relating to the fairness of an investment
in any of the Shares and that no Federal, state, local or foreign governmental
body or regulatory authority has recommended or endorsed, or will recommend or
endorse, any investment in any of the Shares. The Purchaser, in making the
decision to purchase the Shares, has relied upon independent investigation made
by it and has not relied on any information or representations made by third
parties.

                  (d) The Purchaser understands that the Shares are being
offered and sold to it in reliance on specific provisions of Federal and state
securities laws and that the Company is relying upon the truth and accuracy of
the representations, warranties, agreements, acknowledgments and understandings
of the Purchaser set forth herein for purposes of qualifying for exemptions from
registration under the Securities Act, and applicable state securities laws.

                  (e) The Purchaser is an  "accredited  investor" as defined
under Rule 501 of Regulation D promulgated under the Securities Act.

                  (f) The Purchaser is and will be acquiring the Shares for such
Purchaser's own account, and not with a view to any resale or distribution of
the Shares in whole or in part, in violation of the Securities Act or any
applicable securities laws.

                  (g) The offer and sale of the Shares is intended to be exempt
from registration under the Securities Act, by virtue of Section 4(2) and Rule
506 of Regulation D promulgated under the Securities Act. The Purchaser
understands that the Shares purchased hereunder have not been, and may never be,
registered under the Securities Act and that none of the Shares can be sold or
transferred unless they are first registered under the Securities Act and such
state and

<PAGE>

other securities laws as may be applicable or in the opinion of
counsel for the Company an exemption from registration under the Securities Act
is available (and then the Shares may be sold or transferred only in compliance
with such exemption and all applicable state and other securities laws).

                  (h) The Purchaser (i) has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of an investment in the Company; and (ii) recognizes that such Purchaser's
investment in the Company involves a high degree of risk.

                  (i) The Purchaser is capable of evaluating the risks and
merits of an investment in the Shares by virtue of its experience as an investor
and its knowledge, experience, and sophistication in financial and business
matters and such Purchaser is capable of bearing the entire loss of its
investment in the Shares.

                  (j) The Purchaser is neither a registered broker-dealer nor
an affiliate of a registered broker-dealer.

                  (k) The Purchaser and its advisors, if any, have been
furnished with all materials relating to the business, finances and operations
of the Company and materials relating to the offer and sale of the Shares which
have been requested by the Purchaser. The Purchaser and its advisors, if any,
have been afforded the opportunity to ask questions of the Company. The
Purchaser has sought such accounting, legal and tax advice as it has considered
necessary to make an informed investment decision with respect to its
acquisition of the Shares. Purchaser understands that it (and not the Company)
shall be responsible for its own tax liabilities that may arise as a result of
this investment or the transactions contemplated by this Agreement. The
Purchaser has not obtained any material non-public information from the Company.

                  (l) The Purchaser shall comply with all applicable federal
securities laws, rules and regulations in connection with the sale of the Shares
purchased by the Purchase hereunder.

         3.       Representations,  Warranties and Covenants of the Company.
The Company represents and warrants to the Purchaser, and covenants for the
benefit of the Purchaser, as follows:

                  (a) The Company has been duly incorporated and is validly
existing and in good standing under the laws of the state of Delaware, with full
corporate power and authority to own, lease and operate its properties and to
conduct its business as currently conducted, and is duly registered and
qualified to conduct its business and is in good standing in each jurisdiction
or place where the nature of its properties or the conduct of its business
requires such registration or qualification, except where the failure to
register or qualify would not have a Material Adverse Effect. For purposes of
this Agreement, "Material Adverse Effect" shall mean any effect on the business,
results of operations, prospects, assets or financial condition of the Company
that is material and adverse to the Company and its subsidiaries and affiliates,
taken as

<PAGE>

a whole and/or any condition, circumstance, or situation that would
prohibit or otherwise materially interfere with the ability of the Company from
entering into and performing any of its obligations under this Agreement in any
material respect; provided, however, that the foregoing shall not include
operating losses of the Company in the amounts contemplated by the Commission
Documents.

                  (b) The Company has furnished the Purchaser with copies of the
Company's Annual Report on Form 10-K for fiscal year ended March 31, 2001 (the
"Form 10-K") filed with the Securities and Exchange Commission (the
"Commission") and its Form 10-Q for the quarterly period ended December 31, 2001
(the "Form 10-Q"; collectively with the Form 10-K, the "Public Documents"). The
Public Documents at the time of their filing did not include any untrue
statement of a material fact or omit to state any material fact necessary in
order to make the statements contained therein, in light of the circumstances
under which they were made, not misleading. As used herein, "Commission
Documents" means all reports, schedules, forms, statements and other documents
filed by the Company with the Commission after March 31, 2001 pursuant to the
reporting requirements of the Exchange Act, including material filed pursuant to
Section 13(a) or 15(d) of the Exchange Act.

                  (c) The Shares have been duly authorized by all necessary
corporate action and, when paid for by the Purchaser and issued in accordance
with the terms hereof, the Shares shall be validly issued, fully paid and
non-assessable.

                  (d) Each of this Agreement and the Registration Rights
Agreement attached hereto as Exhibit A (the "Registration Rights Agreement") has
been duly authorized, validly executed and delivered on behalf of the Company
and is a valid and binding agreement and obligation of the Company enforceable
against the Company in accordance with its terms, subject to limitations on
enforcement by general principles of equity and by bankruptcy or other laws
affecting the enforcement of creditors' rights generally, and the Company has
full power and authority to execute and deliver this Agreement and the other
agreements and documents contemplated hereby and to perform its obligations
hereunder and thereunder.

                  (e) Except as disclosed in Schedule 3(e) attached hereto, the
execution and delivery of this Agreement and the Registration Rights Agreement,
the issuance of any of the Shares and the consummation of the transactions
contemplated by this Agreement and the Registration Rights Agreement by the
Company, will not (i) conflict with or result in a breach of or a default under
any of the terms or provisions of, (A) the Company's certificate of
incorporation or by-laws, or (B) of any material provision of any indenture,
mortgage, deed of trust or other material agreement or instrument to which the
Company is a party or by which it or any of its material properties or assets is
bound, (ii) result in a violation of any material provision of any law, statute,
rule, regulation, or any existing applicable decree, judgment or order by any
court, Federal or state regulatory body, administrative agency, or other
governmental body having jurisdiction over the Company, or any of its material
properties or assets or (iii) result in the creation or imposition of any
material lien, charge or encumbrance upon any material property or assets of the
Company or any of its subsidiaries pursuant to the terms of any agreement or
instrument to which any of them is a party or by which any of them may be bound

<PAGE>

or to which any of their property or any of them is subject except in the case
of clauses (i)(B) or (iii) for any such conflicts, breaches, or defaults or any
liens, charges, or encumbrances which would not have a Material Adverse Effect.

                  (f) The sale and issuance of the Shares in accordance with the
terms of and in reliance on the accuracy of the Purchaser's representations and
warranties set forth in this Agreement will be exempt from the registration
requirements of the Securities Act.

                  (g) No consent, approval or authorization of or designation,
declaration or filing with any governmental authority on the part of the Company
is required in connection with the valid execution and delivery of this
Agreement or the offer, sale or issuance of the Shares or the consummation of
any other transaction contemplated by this Agreement (other than any filings
which may be required to be made by the Company with the Commission, or the
Nasdaq National Market or pursuant to any state or "blue sky" securities laws
subsequent to the Closing, and, any registration statement which may be filed
pursuant to this Agreement).

                  (h) There is no action, suit, claim, investigation or
proceeding pending or, to the knowledge of the Company, threatened against the
Company which questions the validity of this Agreement or the Registration
Rights Agreement or the transactions contemplated thereby or any action taken or
to be taken pursuant thereto. Except as disclosed in the Commission Documents,
there is no action, suit, claim, investigation or proceeding pending or, to the
knowledge of the Company, threatened, against or involving the Company or any
subsidiary, or any of their respective properties or assets which, if adversely
determined, is reasonably likely to result in a Material Adverse Effect.

                  (i) Subsequent to the dates as of which information is given
in the Public Documents, Commission Documents, this Agreement or the
Registration Rights Agreement and except as contemplated herein, the Company has
not incurred any material liabilities or material obligations, direct or
contingent, or entered into any material transactions not in the ordinary course
of business.

                  (j) The Company has sufficient title and ownership of all
trademarks, service marks, trade names, copyrights, patents, trade secrets and
other proprietary rights ("Intellectual Property") necessary for its business as
now conducted and as proposed to be conducted as described in the Public
Documents or the Commission Documents except for any of the foregoing, the
absence of which would not reasonably be likely to result in a Material Adverse
Effect and, to its knowledge without any conflict with or infringement of the
rights of others. Except as set forth in the Public Documents or the Commission
Documents, there are no material outstanding options, licenses or agreements of
any kind relating to the Intellectual Property, nor is the Company bound by or
party to any material options, licenses or agreements of any kind with respect
to the Intellectual Property of any other person or entity.

                  (k) The Company has complied and will comply with all
applicable federal and state securities laws in connection with the offer,
issuance and sale of the Shares hereunder. Neither the Company nor anyone acting
on its behalf, directly or indirectly, has or will sell, offer

<PAGE>

to sell or solicit offers to buy any of the Shares, or similar securities to,
or solicit offers with respect thereto from, or enter into any preliminary
conversations or negotiations relating thereto with, any person, or has taken
or will take any action so as to bring the issuance and sale of any of the
Shares under the registration provisions of the Securities Act and any other
applicable federal and state securities laws. Neither the Company nor any of
its affiliates, nor any person acting on its or their behalf, has engaged in
any form of general solicitation or general advertising (within the meaning of
Regulation D under the Securities Act) in connection with any of the Shares.

                  (l) To the Company's knowledge, neither this Agreement nor the
Schedules hereto nor the Registration Rights Agreement contain any untrue
statement of a material fact or omit to state a material fact necessary in order
to make the statements made herein or therein, in the light of the circumstances
under which they were made herein or therein, not misleading.

                  (m) The authorized capital stock of the Company and the shares
thereof issued and outstanding as of December 31, 2001 are set forth on Schedule
3(m) attached hereto. All of the outstanding shares of the Company's Common
Stock have been duly and validly authorized, and are fully paid and
non-assessable. Except as set forth in this Agreement, the Public Documents, the
Commission Documents or on Schedule 3(m) attached hereto, as of December 31,
2001, no shares of Common Stock are entitled to preemptive rights or
registration rights and there are no outstanding options, warrants, scrip,
rights to subscribe to, call or commitments of any character whatsoever relating
to, or securities or rights convertible into, any shares of capital stock of the
Company. Furthermore, except as set forth in this Agreement, in the Public
Documents, the Commission Documents or on Schedule 3(m) as of the date hereof,
there are no contracts, commitments, understandings, or arrangements by which
the Company is or may become bound to issue additional shares of the capital
stock of the Company or options, securities or rights convertible into shares of
capital stock of the Company. Except as disclosed in the Commission Documents or
the Public Documents and except for customary transfer restrictions contained in
agreements entered into by the Company in order to sell restricted securities,
as of the date hereof, the Company is not a party to any agreement granting
registration rights to any person with respect to any of its equity or debt
securities. The Company is not a party to, and its executive officers have no
knowledge of, any agreement restricting the voting or transfer of any shares of
the capital stock of the Company. The offer and sale of all capital stock,
convertible securities, rights, warrants, or options of the Company issued prior
to the Closing complied with all applicable federal and state securities laws,
or no stockholder has a right of rescission or damages with respect thereto
which is reasonably likely to have a Material Adverse Effect. The Company has
furnished or made available to the Purchaser true and correct copies of the
Company's Certificate of Incorporation as in effect on the date hereof (the
"Certificate"), and the Company's Bylaws as in effect on the date hereof (the
"Bylaws").

                  (n) Prior to the effectiveness of the Registration Statement
(as defined in the Registration Rights Agreement), the Company will use its
commercially reasonable efforts to list the Shares for trading on the Nasdaq
National Market or any relevant market or system, if applicable, and will comply
in all material respects with the Company's reporting, filing and other

<PAGE>

obligations under the bylaws or rules of the Nasdaq National Market or any
relevant market or system.

                  (o) Except for the disclosure of this Agreement and the
Registration Rights Agreement and information contained therein to the holders
of the Company's 5% subordinated convertible debentures, consistent with the
requirements of the related purchase agreement, the Company may not issue a
press release or otherwise make a public statement or announcement with respect
to the transaction contemplated hereby prior to the Closing Date. In the event
that the Company is required by law or regulations to issue a press release or
otherwise make a public statement or announcement with respect to this Agreement
after the Closing Date, the Company shall consult with the Purchaser on the form
and substance of such press release or other disclosure.

                  (p) Prior to the effectiveness of the Registration Statement,
the Company may enter into an agreement with a third party, the principal
purpose of which is to secure equity financing (an "Other Financing"). If prior
to the effectiveness of the Registration Statement the Company enters into an
Other Financing at a price per share less than the Purchaser's Per Share
Purchase Price, the Company will issue additional shares to the Purchaser based
on standard "weighted average" anti-dilution formula (the "Anti-Dilution
Shares") as set forth on Schedule 3(p) hereof. If issued, the Anti-Dilution
Shares shall, at the Purchaser's option, if appropriate, be registered in a
separate registration statement. As used herein, "Other Financing" shall not
include the Company (i) entering into a loan, credit or lease facility with a
bank or financing institution (including any equity component thereof), (ii)
establishing an employee stock option plan or agreement, (iii) issuing shares of
Common Stock in connection with the Company's option plans (as the same may be
amended from time to time), stock purchase plans, rights plans, currently
outstanding warrants or options (unless the exercise price of such warrants or
options are reset to a price below the current exercise price), or increase the
number of shares available under any such plans (the primary purpose of which is
not to raise equity), (iv) issuing shares of Common Stock upon conversion of the
Company's existing subordinated convertible debentures and series B convertible
preferred stock (unless the conversion price of such debentures or series B
convertible preferred stock are reset (other than by its stated terms) to a
price below the current conversion price) and (v) issuing shares of Common Stock
and/or preferred stock in connection with the formation or maintenance of
strategic partnerships, alliances, licenses or joint ventures and the
acquisition of products, licenses or other assets (each a "Permitted
Transaction").

         4. Conditions Precedent to the Obligation of the Company to Sell the
Shares: The obligation hereunder of the Company to issue and sell the Shares to
the Purchaser is subject to the satisfaction or waiver, at or before the Closing
Date, of each of the conditions set forth below. These conditions are for the
Company's sole benefit and may be waived by the Company at any time in its sole
discretion.

                  (a)The Purchaser shall have executed and delivered this
Agreement and the Registration Rights Agreement.

                  (b) The Purchaser shall have performed, satisfied and complied
in all material respects with all covenants, agreements and conditions required
by this Agreement and the

<PAGE>

Registration Rights Agreement to be performed, satisfied or complied with by
such Purchaser at or prior to the Closing Date.

                  (c) The representations and warranties of the Purchaser shall
be true and correct in all material respects as of the date when made and as of
the Closing Date as though made at that time, except for representations and
warranties that are expressly made as of a particular date, which shall be true
and correct in all material respects as of such date.

                  (d) At the Closing Date, upon receipt of the certificates
evidencing the Shares, the Purchaser shall have delivered to the Company
immediately available funds as payment in full of the Purchase Price for the
Shares.

                  (e) No statute, regulation, executive order, decree, ruling or
injunction shall have been enacted, entered, promulgated or endorsed by any
court or governmental authority of competent jurisdiction which prohibits the
consummation of any of the transactions contemplated by this Agreement at or
prior to the Closing Date.

                  (f) As of the Closing Date, no action, suit or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which questions the validity of the Agreement, the Registration Rights Agreement
or the transactions contemplated thereby or any action taken or to be taken
pursuant thereto.

                  (g) The Company will not be obligated to issue any shares of
Common Stock which would result in the issuance under this Agreement of more
than fourteen and nine-tenths percent (14.9%) of the shares of capital stock
deemed issued and outstanding under the Company's Rights Plan, unless the Board
of Directors has approved such issuance.

         5. Conditions Precedent to the Obligation of the Purchaser to purchase
the Shares: The obligation hereunder of the Purchaser to acquire and pay for the
Shares is subject to the satisfaction or waiver, at or before the Closing Date,
of each of the conditions set forth below. These conditions are for the
Purchaser's sole benefit and may be waived by the Purchaser at any time in its
sole discretion.

                  (a) The Company shall have executed and delivered this
Agreement and the Registration Rights Agreement.

                  (b) The Company shall have performed, satisfied and complied
in all material respects with all covenants, agreements and conditions required
by this Agreement and the Registration Rights Agreement to be performed,
satisfied or complied with by the Company at or prior to the Closing Date.

                  (c) Each of the representations and warranties of the Company
shall be true and correct in all material respects as of the date when made and
as of the Closing Date as

<PAGE>

though made at that time (except for representations and warranties that speak
as of a particular date), which shall be true and correct in all material
respects as of such date.

                  (d) No statute, regulation, executive order, decree, ruling or
injunction shall have been enacted, entered, promulgated or endorsed by any
court or governmental authority of competent jurisdiction which prohibits the
consummation of any of the transactions contemplated by this Agreement at or
prior to the Closing Date.

                  (e) As of the Closing Date, no action, suit or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which questions the validity of the Agreement, the Registration Rights Agreement
or the transactions contemplated thereby or any action taken or to be take
pursuant thereto. As of the Closing Date, no action, suit, claim or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which, if adversely determined, is reasonably likely to result in a Material
Adverse Effect.

                  (f) No Material Adverse Effect shall have occurred at or
before the Closing Date.

                  (g) As of the Closing Date, trading in the Common Stock shall
not have been suspended by the Commission or the Nasdaq National Market or any
alternate market (except for any suspension of trading of limited duration
agreed to by the Company, which suspension shall be terminated prior to the
Closing Date).

                  (h) The Company  shall have  delivered  certificates
evidencing  the Shares to the  Purchaser  at or before the Closing Date.

                  (i) The Company shall have delivered on the Closing Date to
the Purchaser a secretary's certificate, dated as of the Closing Date, as to (i)
the resolutions of the board of directors of the Company authorizing the
transactions contemplated by this Agreement, (ii) the Certificate, (iii) the
Bylaws, each as in effect at the Closing, and (iv) the authority and incumbency
of the officers of the Company executing this Agreement and the Registration
Rights Agreement.

                  (j) The Purchaser shall have received a legal opinion in
substantially the form annexed hereto as Exhibit B as of the Closing Date.

                  (k) The Purchaser will not be obligated to purchase any shares
of Common Stock which would result in the issuance under this Agreement of more
than fourteen and nine-tenths percent (14.9%) of the shares of capital stock
deemed issued and outstanding under the Company's Rights Plan, unless the Board
of Directors has approved such issuance.

<PAGE>

         6.       Legends.  Unless otherwise  provided below, each certificate
representing the Shares shall be stamped or otherwise imprinted with a legend
substantially in the following form (the "Legend"):

        "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
        REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
        "SECURITIES ACT"), OR ANY STATE SECURITIES LAWS AND MAY NOT BE
        SOLD, TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS REGISTERED
        UNDER THE SECURITIES ACT AND UNDER APPLICABLE STATE SECURITIES
        LAWS OR IGEN INTERNATIONAL, INC. (THE "COMPANY") SHALL HAVE
        RECEIVED AN OPINION FROM COUNSEL TO THE COMPANY, IN FORM,
        SCOPE AND SUBSTANCE REASONABLY ACCEPTABLE TO THE COMPANY THAT
        REGISTRATION OF SUCH SECURITIES UNDER THE SECURITIES ACT AND
        UNDER THE PROVISIONS OF APPLICABLE FEDERAL AND STATE
        SECURITIES LAWS IS NOT REQUIRED."

         7. Fees and Expenses. Each of the Company and the Purchaser shall pay
its respective fees and expenses related to the transactions contemplated by
this Agreement and the Registration Rights Agreement. Neither the Company nor
the Purchaser has employed, or is subject to the valid claim of, any broker,
finder, investment banker, consultant, financial advisor or other intermediary
(collectively "Broker") in connection with the transactions contemplated by this
Agreement who might be entitled to a fee or commission in connection with this
Agreement or the transactions contemplated hereby. Each party agrees to and
shall indemnify the other against any claim for a fee or commission made by any
Broker against the other in connection with this Agreement or the transactions
contemplated hereby.

         8.       Indemnification.

                  (a) The Company hereby agrees to indemnify and hold harmless
the Purchaser and its officers, directors, shareholders, employees, agents and
attorneys against any and all losses, claims, damages, liabilities and
reasonable expenses (collectively "Claims") incurred by each such person in
connection with defending or investigating any such Claims, whether or not
resulting in any liability to such person, to which any such indemnified party
may become subject, insofar as such Claims arise out of or are based upon any
breach of any representation or warranty or agreement made by the Company in
this Agreement.

                  (b) The Purchaser hereby agrees to indemnify and hold harmless
the Company and its officers, directors, shareholders, employees, agents and
attorneys against any and all losses, claims, damages, liabilities and expenses
incurred by each such person in connection with defending or investigating any
such claims or liabilities, whether or not resulting

<PAGE>

in any liability to such person, to which any such indemnified party may become
subject under the Securities Act, or under any other statute, at common law or
otherwise, insofar as such Claims arise out of or are based upon (i) any untrue
statement or alleged untrue statement of a material fact made by the Purchaser,
(ii) any omission or alleged omission of a material fact with respect to the
Purchaser or (iii) any breach of any representation, warranty or agreement made
by the Purchaser in this Agreement.

         9. Governing Law; Consent to Jurisdiction. This Agreement shall be
governed by and interpreted in accordance with the laws of the State of New York
without giving effect to the rules governing the conflicts of laws. Each of the
parties consents to the exclusive jurisdiction of the Federal courts whose
districts encompass any part of the County of New York located in the City of
New York in connection with any dispute arising under this Agreement and hereby
waives, to the maximum extent permitted by law, any objection, including any
objection based on forum non conveniens, to the bringing of any such proceeding
in such jurisdictions. Each party waives its right to a trial by jury. Each
party to this Agreement irrevocably consents to the service of process in any
such proceeding by the mailing of copies thereof by registered or certified
mail, postage prepaid, to such party at its address set forth herein. Nothing
herein shall affect the right of any party to serve process in any other manner
permitted by law.

         10. Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, express overnight
courier, registered first class mail, or telecopier (provided that any notice
sent by telecopier shall be confirmed by other means pursuant to this Section
10), initially to the address set forth below, and thereafter at such other
address, notice of which is given in accordance with the provisions of this
Section.

                  (a)      if to the Company:

                           IGEN International, Inc.
                           16020 Industrial Drive
                           Gaithersburg, MD 20877
                           Tel. No.:  (301) 869-9800
                           Fax No.:  (301) 208-3799
                           Attention: Richard Massey

                           with a copy to:

                           Kirkpatrick & Lockhart LLP
                           1800 Massachusetts Avenue, N.W.
                           Suite 200
                           Washington, D.C. 20036
                           Tel. No.:  (202) 778-9076
                           Fax No.:  (202) 778-9100
                           Attention: Thomas F. Cooney, III

<PAGE>

                   (b)      if to the Purchaser:

                           Acqua Wellington Private Placement Fund, Ltd.
                           c/o Fortis Fund Services (Bahamas) Ltd.
                           Montague Sterling Centre
                           East Bay Street, P. O. Box SS-6238
                           Nassau, Bahamas
                           Attention:  Anthony L.M. Inder Rieden
                           Tel. No.: (242) 394-2700
                           Fax No.: (242) 394-9667

                           with a copy to:

                           Jenkens & Gilchrist Parker Chapin LLP
                           The Chrysler Building
                           405 Lexington Avenue
                           New York, New York 10174
                           Attention:  Christopher S. Auguste
                           Tel. No.: (212) 704-6000
                           Fax No.: (212) 704-6288

         All such notices and communications shall be deemed to have been duly
given: when delivered by hand, if personally delivered; when receipt is
acknowledged, if telecopied; or when actually received or refused if sent by
other means.

         11. Entire Agreement. This Agreement and the Registration Rights
Agreement constitute the entire understanding and agreement of the parties with
respect to the subject matter hereof and supersedes all prior and/or
contemporaneous oral or written proposals or agreements relating thereto all of
which are merged herein. This Agreement may not be amended or any provision
hereof waived in whole or in part, except by a written amendment signed by both
of the parties.

         12.      Counterparts.  This  Agreement  may be executed by facsimile
signature and in counterparts, each of which shall be deemed an original, but
all of which together shall constitute one and the same instrument.

                                  [end of page]

<PAGE>

         IN WITNESS WHEREOF, this Agreement was duly executed on the date first
written above.

                            IGEN INTERNATIONAL, INC.

                            By:  /s/ Samuel J. Wohlstadter
                            ----------------------------------
                            Name:    Samuel J. Wohlstadter
                            Title:   Chief Executive Officer

                            ACQUA WELLINGTON PRIVATE PLACEMENT FUND, LTD.

                            By:   /s/ Richard Perry Pinder
                            ---------------------------------
                            Name:    Richard Perry Pinder
                            Title:   Vice PresidentExhibit 10.2

                               PURCHASE AGREEMENT

         This PURCHASE AGREEMENT (this "Agreement"), dated as of March 8, 2002,
is entered into by and between IGEN International, Inc., a Delaware corporation
(the "Company"), and Acqua Wellington Opportunity I Limited, a company organized
under the laws of the Commonwealth of the Bahamas (the "Purchaser"), for the
purchase and sale of shares of the common stock, par value $.001 per share (the
"Common Stock"), of the Company by the Purchaser, in the manner, and upon the
terms, provisions and conditions set forth in this Agreement.

         WHEREAS, the parties desire that, upon the terms and subject to the
conditions contained herein, the Company shall issue and sell to the Purchaser
and Purchaser shall purchase shares of Common Stock; and

         WHEREAS, such purchase and sale will be made in reliance upon the
provisions of Section 4(2) and Rule 506 of Regulation D ("Regulation D") of the
United States Securities Act of 1933, as amended, and regulations promulgated
thereunder (the "Securities Act"), or upon such other exemption from the
registration requirements of the Securities Act as may be available with respect
to any or all of the purchases of Common Stock to be made hereunder.

         NOW, THEREFORE, in consideration of the representations, warranties and
agreements contained herein and other good and valuable consideration, the
receipt and legal adequacy of which is hereby acknowledged by the parties, the
Company and the Purchaser hereby agree as follows:

         1.       Purchase Price.

                  (a) Upon the following terms and subject to the conditions
contained herein, the Purchaser hereby agrees to purchase 440,000 shares of the
Company's Common Stock (the "Shares") at a per share price of $36.8094 ("Per
Share Purchase Price") and for an aggregate purchase price of $16,196,136 (the
"Purchase Price").

                  (b) The Company has authorized and has reserved and covenants
to continue to reserve, free of preemptive rights and other similar contractual
rights of stockholders, a sufficient number of its authorized but unissued
shares of Common Stock, to effect the issuance of the Shares.

                  (c) In consideration of and in express reliance upon the
representations, warranties, covenants, terms and conditions of this Agreement,
the Company agrees to issue and sell to the Purchaser and the Purchaser agrees
to purchase the Shares. The closing under this Agreement (the "Closing") shall
take place at the offices of Jenkens & Gilchrist Parker Chapin LLP, The Chrysler
Building, 405 Lexington Avenue, New York, New York 10174 at 1:00 p.m. on March
11, 2002 (eastern time)

<PAGE>

upon the satisfaction of each of the conditions set forth in Sections 4 and 5
hereof (the "Closing Date").

         2.       Representations, Warranties and Covenants of the Purchaser.
The Purchaser represents and warrants to the Company, and covenants for the
benefit of the Company, as follows:

                  (a) The Purchaser is a limited liability company duly
organized, validly existing and in good standing under the laws of the
Commonwealth of The Bahamas.

                  (b) This Agreement has been duly authorized, validly executed
and delivered by the Purchaser and is a valid and binding agreement and
obligation of the Purchaser enforceable against the Purchaser in accordance with
its terms, subject to limitations on enforcement by general principles of equity
and by bankruptcy or other laws affecting the enforcement of creditors' rights
generally, and the Purchaser has full power and authority to execute and deliver
this Agreement and the other agreements and documents contemplated hereby and to
perform its obligations hereunder and thereunder.

                  (c) The Purchaser has received and carefully reviewed copies
of the Public Documents (as hereinafter defined). The Purchaser understands that
no Federal, state, local or foreign governmental body or regulatory authority
has made any finding or determination relating to the fairness of an investment
in any of the Shares and that no Federal, state, local or foreign governmental
body or regulatory authority has recommended or endorsed, or will recommend or
endorse, any investment in any of the Shares. The Purchaser, in making the
decision to purchase the Shares, has relied upon independent investigation made
by it and has not relied on any information or representations made by third
parties.

                  (d) The Purchaser understands that the Shares are being
offered and sold to it in reliance on specific provisions of Federal and state
securities laws and that the Company is relying upon the truth and accuracy of
the representations, warranties, agreements, acknowledgments and understandings
of the Purchaser set forth herein for purposes of qualifying for exemptions from
registration under the Securities Act, and applicable state securities laws.

                  (e) The Purchaser is an  "accredited  investor" as defined
under Rule 501 of Regulation D promulgated under the Securities Act.

                  (f) The Purchaser is and will be acquiring the Shares for such
Purchaser's own account, and not with a view to any resale or distribution of
the Shares in whole or in part, in violation of the Securities Act or any
applicable securities laws.

                  (g) The offer and sale of the Shares is intended to be exempt
from registration under the Securities Act, by virtue of Section 4(2) and Rule
506 of Regulation D promulgated under the Securities Act. The Purchaser
understands that the Shares purchased hereunder have not been, and may never be,
registered under the Securities Act and that none of the Shares can be sold or
transferred unless they are first registered under the Securities Act and such

<PAGE>

state and other securities laws as may be applicable or in the opinion of
counsel for the Company an exemption from registration under the Securities Act
is available (and then the Shares may be sold or transferred only in compliance
with such exemption and all applicable state and other securities laws).

                  (h) The Purchaser (i) has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of an investment in the Company; and (ii) recognizes that such Purchaser's
investment in the Company involves a high degree of risk.

                  (i) The Purchaser is capable of evaluating the risks and
merits of an investment in the Shares by virtue of its experience as an investor
and its knowledge, experience, and sophistication in financial and business
matters and such Purchaser is capable of bearing the entire loss of its
investment in the Shares.

                  (j) The Purchaser is neither a registered broker-dealer nor
an affiliate of a registered broker-dealer.

                  (k) The Purchaser and its advisors, if any, have been
furnished with all materials relating to the business, finances and operations
of the Company and materials relating to the offer and sale of the Shares which
have been requested by the Purchaser. The Purchaser and its advisors, if any,
have been afforded the opportunity to ask questions of the Company. The
Purchaser has sought such accounting, legal and tax advice as it has considered
necessary to make an informed investment decision with respect to its
acquisition of the Shares. Purchaser understands that it (and not the Company)
shall be responsible for its own tax liabilities that may arise as a result of
this investment or the transactions contemplated by this Agreement. The
Purchaser has not obtained any material non-public information from the Company.

                  (l) The Purchaser shall comply with all applicable federal
securities laws, rules and regulations in connection with the sale of the Shares
purchased by the Purchase hereunder.

         3.       Representations,  Warranties and Covenants of the Company.
The Company represents and warrants to the Purchaser, and covenants for the
benefit of the Purchaser, as follows:

                  (a) The Company has been duly incorporated and is validly
existing and in good standing under the laws of the state of Delaware, with full
corporate power and authority to own, lease and operate its properties and to
conduct its business as currently conducted, and is duly registered and
qualified to conduct its business and is in good standing in each jurisdiction
or place where the nature of its properties or the conduct of its business
requires such registration or qualification, except where the failure to
register or qualify would not have a Material Adverse Effect. For purposes of
this Agreement, "Material Adverse Effect" shall mean any effect on the business,
results of operations, prospects, assets or financial condition of the Company
that is material and adverse to the Company and its subsidiaries and affiliates,

<PAGE>

taken as a whole and/or any condition, circumstance, or situation that would
prohibit or otherwise materially interfere with the ability of the Company from
entering into and performing any of its obligations under this Agreement in any
material respect; provided, however, that the foregoing shall not include
operating losses of the Company in the amounts contemplated by the Commission
Documents.

                  (b) The Company has furnished the Purchaser with copies of the
Company's Annual Report on Form 10-K for fiscal year ended March 31, 2001 (the
"Form 10-K") filed with the Securities and Exchange Commission (the
"Commission") and its Form 10-Q for the quarterly period ended December 31, 2001
(the "Form 10-Q"; collectively with the Form 10-K, the "Public Documents"). The
Public Documents at the time of their filing did not include any untrue
statement of a material fact or omit to state any material fact necessary in
order to make the statements contained therein, in light of the circumstances
under which they were made, not misleading. As used herein, "Commission
Documents" means all reports, schedules, forms, statements and other documents
filed by the Company with the Commission after March 31, 2001 pursuant to the
reporting requirements of the Exchange Act, including material filed pursuant to
Section 13(a) or 15(d) of the Exchange Act.

                  (c) The Shares have been duly authorized by all necessary
corporate action and, when paid for by the Purchaser and issued in accordance
with the terms hereof, the Shares shall be validly issued, fully paid and
non-assessable.

                  (d) Each of this Agreement and the Registration Rights
Agreement attached hereto as Exhibit A (the "Registration Rights Agreement") has
been duly authorized, validly executed and delivered on behalf of the Company
and is a valid and binding agreement and obligation of the Company enforceable
against the Company in accordance with its terms, subject to limitations on
enforcement by general principles of equity and by bankruptcy or other laws
affecting the enforcement of creditors' rights generally, and the Company has
full power and authority to execute and deliver this Agreement and the other
agreements and documents contemplated hereby and to perform its obligations
hereunder and thereunder.

                  (e) Except as disclosed in Schedule 3(e) attached hereto, the
execution and delivery of this Agreement and the Registration Rights Agreement,
the issuance of any of the Shares and the consummation of the transactions
contemplated by this Agreement and the Registration Rights Agreement by the
Company, will not (i) conflict with or result in a breach of or a default under
any of the terms or provisions of, (A) the Company's certificate of
incorporation or by-laws, or (B) of any material provision of any indenture,
mortgage, deed of trust or other material agreement or instrument to which the
Company is a party or by which it or any of its material properties or assets is
bound, (ii) result in a violation of any material provision of any law, statute,
rule, regulation, or any existing applicable decree, judgment or order by any
court, Federal or state regulatory body, administrative agency, or other
governmental body having jurisdiction over the Company, or any of its material
properties or assets or (iii) result in the creation or imposition of any
material lien, charge or encumbrance upon any material property or assets of the
Company or any of its subsidiaries pursuant to the terms of any agreement or
instrument to which any of them is a party or by which any of them may be bound

<PAGE>

or to which any of their property or any of them is subject except in the case
of clauses (i)(B) or (iii) for any such conflicts, breaches, or defaults or any
liens, charges, or encumbrances which would not have a Material Adverse Effect.

                  (f) The sale and issuance of the Shares in accordance with the
terms of and in reliance on the accuracy of the Purchaser's representations and
warranties set forth in this Agreement will be exempt from the registration
requirements of the Securities Act.

                  (g) No consent, approval or authorization of or designation,
declaration or filing with any governmental authority on the part of the Company
is required in connection with the valid execution and delivery of this
Agreement or the offer, sale or issuance of the Shares or the consummation of
any other transaction contemplated by this Agreement (other than any filings
which may be required to be made by the Company with the Commission, or the
Nasdaq National Market or pursuant to any state or "blue sky" securities laws
subsequent to the Closing, and, any registration statement which may be filed
pursuant to this Agreement).

                  (h) There is no action, suit, claim, investigation or
proceeding pending or, to the knowledge of the Company, threatened against the
Company which questions the validity of this Agreement or the Registration
Rights Agreement or the transactions contemplated thereby or any action taken or
to be taken pursuant thereto. Except as disclosed in the Commission Documents,
there is no action, suit, claim, investigation or proceeding pending or, to the
knowledge of the Company, threatened, against or involving the Company or any
subsidiary, or any of their respective properties or assets which, if adversely
determined, is reasonably likely to result in a Material Adverse Effect.

                  (i) Subsequent to the dates as of which information is given
in the Public Documents, Commission Documents, this Agreement or the
Registration Rights Agreement and except as contemplated herein, the Company has
not incurred any material liabilities or material obligations, direct or
contingent, or entered into any material transactions not in the ordinary course
of business.

                  (j) The Company has sufficient title and ownership of all
trademarks, service marks, trade names, copyrights, patents, trade secrets and
other proprietary rights ("Intellectual Property") necessary for its business as
now conducted and as proposed to be conducted as described in the Public
Documents or the Commission Documents except for any of the foregoing, the
absence of which would not reasonably be likely to result in a Material Adverse
Effect and, to its knowledge without any conflict with or infringement of the
rights of others. Except as set forth in the Public Documents or the Commission
Documents, there are no material outstanding options, licenses or agreements of
any kind relating to the Intellectual Property, nor is the Company bound by or
party to any material options, licenses or agreements of any kind with respect
to the Intellectual Property of any other person or entity.

                  (k) The Company has complied and will comply with all
applicable federal and state securities laws in connection with the offer,
issuance and sale of the Shares hereunder. Neither the Company nor anyone acting
on its behalf, directly or indirectly, has or will sell, offer to sell or

<PAGE>

solicit offers to buy any of the Shares, or similar securities to, or solicit
offers with respect thereto from, or enter into any preliminary conversations or
negotiations relating thereto with, any person, or has taken or will take any
action so as to bring the issuance and sale of any of the Shares under the
registration provisions of the Securities Act and any other applicable federal
and state securities laws. Neither the Company nor any of its affiliates, nor
any person acting on its or their behalf, has engaged in any form of general
solicitation or general advertising (within the meaning of Regulation D under
the Securities Act) in connection with any of the Shares.

                  (l) To the Company's knowledge, neither this Agreement nor the
Schedules hereto nor the Registration Rights Agreement contain any untrue
statement of a material fact or omit to state a material fact necessary in order
to make the statements made herein or therein, in the light of the circumstances
under which they were made herein or therein, not misleading.

                  (m) The authorized capital stock of the Company and the shares
thereof issued and outstanding as of December 31, 2001 are set forth on Schedule
3(m) attached hereto. All of the outstanding shares of the Company's Common
Stock have been duly and validly authorized, and are fully paid and
non-assessable. Except as set forth in this Agreement, the Public Documents, the
Commission Documents or on Schedule 3(m) attached hereto, as of December 31,
2001, no shares of Common Stock are entitled to preemptive rights or
registration rights and there are no outstanding options, warrants, scrip,
rights to subscribe to, call or commitments of any character whatsoever relating
to, or securities or rights convertible into, any shares of capital stock of the
Company. Furthermore, except as set forth in this Agreement, in the Public
Documents, the Commission Documents or on Schedule 3(m) as of the date hereof,
there are no contracts, commitments, understandings, or arrangements by which
the Company is or may become bound to issue additional shares of the capital
stock of the Company or options, securities or rights convertible into shares of
capital stock of the Company. Except as disclosed in the Commission Documents or
the Public Documents and except for customary transfer restrictions contained in
agreements entered into by the Company in order to sell restricted securities,
as of the date hereof, the Company is not a party to any agreement granting
registration rights to any person with respect to any of its equity or debt
securities. The Company is not a party to, and its executive officers have no
knowledge of, any agreement restricting the voting or transfer of any shares of
the capital stock of the Company. The offer and sale of all capital stock,
convertible securities, rights, warrants, or options of the Company issued prior
to the Closing complied with all applicable federal and state securities laws,
or no stockholder has a right of rescission or damages with respect thereto
which is reasonably likely to have a Material Adverse Effect. The Company has
furnished or made available to the Purchaser true and correct copies of the
Company's Certificate of Incorporation as in effect on the date hereof (the
"Certificate"), and the Company's Bylaws as in effect on the date hereof (the
"Bylaws").

                  (n) Prior to the effectiveness of the Registration Statement
(as defined in the Registration Rights Agreement), the Company will use its
commercially reasonable efforts to list the Shares for trading on the Nasdaq
National Market or any relevant market or system, if applicable, and will comply
in all material respects with the Company's reporting, filing and other

<PAGE>

obligations under the bylaws or rules of the Nasdaq National Market or any
relevant market or system.

                  (o) Except for the disclosure of this Agreement and the
Registration Rights Agreement and information contained therein to the holders
of the Company's 5% subordinated convertible debentures, consistent with the
requirements of the related purchase agreement, the Company may not issue a
press release or otherwise make a public statement or announcement with respect
to the transaction contemplated hereby prior to the Closing Date. In the event
that the Company is required by law or regulations to issue a press release or
otherwise make a public statement or announcement with respect to this Agreement
after the Closing Date, the Company shall consult with the Purchaser on the form
and substance of such press release or other disclosure.

                  (p) Prior to the effectiveness of the Registration Statement,
the Company may enter into an agreement with a third party, the principal
purpose of which is to secure equity financing (an "Other Financing"). If prior
to the effectiveness of the Registration Statement the Company enters into an
Other Financing at a price per share less than the Purchaser's Per Share
Purchase Price, the Company will issue additional shares to the Purchaser based
on standard "weighted average" anti-dilution formula (the "Anti-Dilution
Shares") as set forth on Schedule 3(p) hereof. If issued, the Anti-Dilution
Shares shall, at the Purchaser's option, if appropriate, be registered in a
separate registration statement. As used herein, "Other Financing" shall not
include the Company (i) entering into a loan, credit or lease facility with a
bank or financing institution (including any equity component thereof), (ii)
establishing an employee stock option plan or agreement, (iii) issuing shares of
Common Stock in connection with the Company's option plans (as the same may be
amended from time to time), stock purchase plans, rights plans, currently
outstanding warrants or options (unless the exercise price of such warrants or
options are reset to a price below the current exercise price), or increase the
number of shares available under any such plans (the primary purpose of which is
not to raise equity), (iv) issuing shares of Common Stock upon conversion of the
Company's existing subordinated convertible debentures and series B convertible
preferred stock (unless the conversion price of such debentures or series B
convertible preferred stock are reset (other than by its stated terms) to a
price below the current conversion price) and (v) issuing shares of Common Stock
and/or preferred stock in connection with the formation or maintenance of
strategic partnerships, alliances, licenses or joint ventures and the
acquisition of products, licenses or other assets (each a "Permitted
Transaction").

         4. Conditions Precedent to the Obligation of the Company to Sell the
Shares: The obligation hereunder of the Company to issue and sell the Shares to
the Purchaser is subject to the satisfaction or waiver, at or before the Closing
Date, of each of the conditions set forth below. These conditions are for the
Company's sole benefit and may be waived by the Company at any time in its sole
discretion.

                  (a) The Purchaser shall have executed and delivered this
Agreement and the Registration Rights Agreement.

                  (b) The Purchaser shall have performed, satisfied and complied
in all material respects with all covenants, agreements and conditions required

<PAGE>

by this Agreement and the Registration Rights Agreement to be performed,
satisfied or complied with by such Purchaser at or prior to the Closing Date.

                  (c) The representations and warranties of the Purchaser shall
be true and correct in all material respects as of the date when made and as of
the Closing Date as though made at that time, except for representations and
warranties that are expressly made as of a particular date, which shall be true
and correct in all material respects as of such date.

                  (d) At the Closing Date, upon receipt of the certificates
evidencing the Shares, the Purchaser shall have delivered to the Company
immediately available funds as payment in full of the Purchase Price for the
Shares.

                  (e) No statute, regulation, executive order, decree, ruling or
injunction shall have been enacted, entered, promulgated or endorsed by any
court or governmental authority of competent jurisdiction which prohibits the
consummation of any of the transactions contemplated by this Agreement at or
prior to the Closing Date.

                  (f) As of the Closing Date, no action, suit or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which questions the validity of the Agreement, the Registration Rights Agreement
or the transactions contemplated thereby or any action taken or to be taken
pursuant thereto.

                  (g) The Company will not be obligated to issue any shares of
Common Stock which would result in the issuance under this Agreement of more
than fourteen and nine-tenths percent (14.9%) of the shares of capital stock
deemed issued and outstanding under the Company's Rights Plan, unless the Board
of Directors has approved such issuance.

         5. Conditions Precedent to the Obligation of the Purchaser to purchase
the Shares: The obligation hereunder of the Purchaser to acquire and pay for the
Shares is subject to the satisfaction or waiver, at or before the Closing Date,
of each of the conditions set forth below. These conditions are for the
Purchaser's sole benefit and may be waived by the Purchaser at any time in its
sole discretion.

                  (a) The Company shall have executed and delivered this
Agreement and the Registration Rights Agreement.

                  (b) The Company shall have performed, satisfied and complied
in all material respects with all covenants, agreements and conditions required
by this Agreement and the Registration Rights Agreement to be performed,
satisfied or complied with by the Company at or prior to the Closing Date.

                  (c) Each of the representations and warranties of the Company
shall be true and correct in all material respects as of the date when made and

<PAGE>

as of the Closing Date as though made at that time (except for representations
and warranties that speak as of a particular date), which shall be true and
correct in all material respects as of such date.

                  (d) No statute, regulation, executive order, decree, ruling or
injunction shall have been enacted, entered, promulgated or endorsed by any
court or governmental authority of competent jurisdiction which prohibits the
consummation of any of the transactions contemplated by this Agreement at or
prior to the Closing Date.

                  (e) As of the Closing Date, no action, suit or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which questions the validity of the Agreement, the Registration Rights Agreement
or the transactions contemplated thereby or any action taken or to be take
pursuant thereto. As of the Closing Date, no action, suit, claim or proceeding
before or by any court or governmental agency or body, domestic or foreign,
shall be pending against or affecting the Company, or any of its properties,
which, if adversely determined, is reasonably likely to result in a Material
Adverse Effect.

                  (f) No Material Adverse Effect shall have occurred at or
before the Closing Date.

                  (g) As of the Closing Date, trading in the Common Stock shall
not have been suspended by the Commission or the Nasdaq National Market or any
alternate market (except for any suspension of trading of limited duration
agreed to by the Company, which suspension shall be terminated prior to the
Closing Date).

                  (h) The Company  shall have  delivered  certificates
evidencing  the Shares to the  Purchaser  at or before the Closing Date.

                  (i) The Company shall have delivered on the Closing Date to
the Purchaser a secretary's certificate, dated as of the Closing Date, as to (i)
the resolutions of the board of directors of the Company authorizing the
transactions contemplated by this Agreement, (ii) the Certificate, (iii) the
Bylaws, each as in effect at the Closing, and (iv) the authority and incumbency
of the officers of the Company executing this Agreement and the Registration
Rights Agreement.

                  (j) The Purchaser shall have received a legal opinion in
substantially the form annexed hereto as Exhibit B as of the Closing Date.

                  (k) The Purchaser will not be obligated to purchase any shares
of Common Stock which would result in the issuance under this Agreement of more
than fourteen and nine-tenths percent (14.9%) of the shares of capital stock
deemed issued and outstanding under the Company's Rights Plan, unless the Board
of Directors has approved such issuance.
<PAGE>

         6.       Legends.  Unless otherwise  provided below, each certificate
representing the Shares shall be stamped or otherwise imprinted with a legend
substantially in the following form (the "Legend"):

       "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
       REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
       "SECURITIES ACT"), OR ANY STATE SECURITIES LAWS AND MAY NOT BE
       SOLD, TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS REGISTERED
       UNDER THE SECURITIES ACT AND UNDER APPLICABLE STATE SECURITIES
       LAWS OR IGEN INTERNATIONAL, INC. (THE "COMPANY") SHALL HAVE
       RECEIVED AN OPINION FROM COUNSEL TO THE COMPANY, IN FORM,
       SCOPE AND SUBSTANCE REASONABLY ACCEPTABLE TO THE COMPANY THAT
       REGISTRATION OF SUCH SECURITIES UNDER THE SECURITIES ACT AND
       UNDER THE PROVISIONS OF APPLICABLE FEDERAL AND STATE
       SECURITIES LAWS IS NOT REQUIRED."

         7. Fees and Expenses. Each of the Company and the Purchaser shall pay
its respective fees and expenses related to the transactions contemplated by
this Agreement and the Registration Rights Agreement. Neither the Company nor
the Purchaser has employed, or is subject to the valid claim of, any broker,
finder, investment banker, consultant, financial advisor or other intermediary
(collectively "Broker") in connection with the transactions contemplated by this
Agreement who might be entitled to a fee or commission in connection with this
Agreement or the transactions contemplated hereby. Each party agrees to and
shall indemnify the other against any claim for a fee or commission made by any
Broker against the other in connection with this Agreement or the transactions
contemplated hereby.

         8.       Indemnification.

                  (a) The Company hereby agrees to indemnify and hold harmless
the Purchaser and its officers, directors, shareholders, employees, agents and
attorneys against any and all losses, claims, damages, liabilities and
reasonable expenses (collectively "Claims") incurred by each such person in
connection with defending or investigating any such Claims, whether or not
resulting in any liability to such person, to which any such indemnified party
may become subject, insofar as such Claims arise out of or are based upon any
breach of any representation or warranty or agreement made by the Company in
this Agreement.

                  (b) The Purchaser hereby agrees to indemnify and hold harmless
the Company and its officers, directors, shareholders, employees, agents and
attorneys against any and all losses, claims, damages, liabilities and expenses
incurred by each such person in connection with defending or investigating any
such claims or liabilities, whether or not resulting in any liability to such

<PAGE>

person, to which any such indemnified party may become subject under the
Securities Act, or under any other statute, at common law or otherwise, insofar
as such Claims arise out of or are based upon (i) any untrue statement or
alleged untrue statement of a material fact made by the Purchaser, (ii) any
omission or alleged omission of a material fact with respect to the Purchaser or
(iii) any breach of any representation, warranty or agreement made by the
Purchaser in this Agreement.

         9. Governing Law; Consent to Jurisdiction. This Agreement shall be
governed by and interpreted in accordance with the laws of the State of New York
without giving effect to the rules governing the conflicts of laws. Each of the
parties consents to the exclusive jurisdiction of the Federal courts whose
districts encompass any part of the County of New York located in the City of
New York in connection with any dispute arising under this Agreement and hereby
waives, to the maximum extent permitted by law, any objection, including any
objection based on forum non conveniens, to the bringing of any such proceeding
in such jurisdictions. Each party waives its right to a trial by jury. Each
party to this Agreement irrevocably consents to the service of process in any
such proceeding by the mailing of copies thereof by registered or certified
mail, postage prepaid, to such party at its address set forth herein. Nothing
herein shall affect the right of any party to serve process in any other manner
permitted by law.

         10. Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, express overnight
courier, registered first class mail, or telecopier (provided that any notice
sent by telecopier shall be confirmed by other means pursuant to this Section
10), initially to the address set forth below, and thereafter at such other
address, notice of which is given in accordance with the provisions of this
Section.

                  (a)      if to the Company:

                           IGEN International, Inc.
                           16020 Industrial Drive
                           Gaithersburg, MD 20877
                           Tel. No.:  (301) 869-9800
                           Fax No.:  (301) 208-3799
                           Attention: Richard Massey

                           with a copy to:

                           Kirkpatrick & Lockhart LLP
                           1800 Massachusetts Avenue, N.W.
                           Suite 200
                           Washington, D.C. 20036
                           Tel. No.:  (202) 778-9076
                           Fax No.:  (202) 778-9100
                           Attention: Thomas F. Cooney, III

<PAGE>

                  (b)      if to the Purchaser:

                           Acqua Wellington Opportunity I Limited
                           Shirlaw House
                           87 Shirley Street
                           P.O. Box SS-19084
                           Nassau, Bahamas
                           Attention: Michael Taylor
                           Fax No.: (242) 328-6919

                           with a copy to:

                           Jenkens & Gilchrist Parker Chapin LLP
                           The Chrysler Building
                           405 Lexington Avenue
                           New York, New York 10174
                           Attention:  Christopher S. Auguste
                           Tel. No.: (212) 704-6000
                           Fax No.: (212) 704-6288

         All such notices and communications shall be deemed to have been duly
given: when delivered by hand, if personally delivered; when receipt is
acknowledged, if telecopied; or when actually received or refused if sent by
other means.

         11. Entire Agreement. This Agreement and the Registration Rights
Agreement constitute the entire understanding and agreement of the parties with
respect to the subject matter hereof and supersedes all prior and/or
contemporaneous oral or written proposals or agreements relating thereto all of
which are merged herein. This Agreement may not be amended or any provision
hereof waived in whole or in part, except by a written amendment signed by both
of the parties.

         12.      Counterparts.  This  Agreement  may be executed by facsimile
signature and in counterparts, each of which shall be deemed an original, but
all of which together shall constitute one and the same instrument.

                                  [end of page]

<PAGE>

         IN WITNESS WHEREOF, this Agreement was duly executed on the date first
written above.

                            IGEN INTERNATIONAL, INC.

                             By:      /s/ Samuel J. Wohlstadter
                             ----------------------------------
                             Name:    Samuel J. Wohlstadter
                             Title:   Chief Executive Officer

                             ACQUA WELLINGTON OPPORTUNITY I LIMITED

                             By:      /s/ M. W. Taylor
                             --------------------------
                             Name:    M. W. Taylor
                             Title:   Director

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