Document:

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                                                                   Exhibit 10.14
                                   EXHIBIT A
                                   AMENDMENT
                                       TO
                IGEN INTERNATIONAL, INC. 1994 STOCK OPTION PLAN

    The following section of the IGEN International, Inc. 1994 Stock Option Plan
(the "1994 Plan") was amended effective July 24, 1998 (subject to shareholder
approval).

    New language in the 1994 Plan is shown in double underline, deleted language
is shown in <#>strikeout</#>, and language that is unchanged is indicated by
plain text; PROVIDED, HOWEVER, that the deleted language and double underling
are for convenience only and are not part of the Plan as amended:

    Section 4, as amended reads:

4. SHARES SUBJECT TO THE PLAN.

    a. Subject to the provisions of Section 10 relating to adjustments upon
changes in stock, the stock that may be sold pursuant to Options shall not
exceed in the aggregate <#>one million (1,000,000)</#> ONE MILLION SEVEN HUNDRED
FIFTY THOUSAND (1,750,000) shares of the Company's common stock. If any Option
shall for any reason expire or otherwise terminate, in whole or in part, without
having been exercised in full, the stock not purchased under such Option shall
revert to and again become available for issuance under the Plan.

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                                   APPENDIX A

                            IGEN INTERNATIONAL, INC.

                             1994 STOCK OPTION PLAN

                           AS AMENDED JULY 24, 1998.

    THIS DOCUMENT IS SUBMITTED PURSUANT TO RULE 14A, ITEM 10, INSTRUCTION 3
                  AND WILL NOT BE DISTRIBUTED TO SHAREHOLDERS.

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                            IGEN INTERNATIONAL, INC,
                             1994 STOCK OPTION PLAN
                            AS AMENDED JULY 24, 1998

1. PURPOSES.

    (a) The purpose of the Plan is to provide a means by which selected
Employees of and Consultants to the Company, and its Affiliates, may be given an
opportunity to purchase stock of the Company.

    (b) The Company, by means of the Plan, seeks to retain the services of
persons who are now Employees of or Consultants to the Company or its
Affiliates, to secure and retain the services of new Employees and Consultants,
and to provide incentives for such persons to exert maximum efforts for the
success of the Company and its Affiliates.

    (c) The Company intends that the Options issued under the Plan shall, in the
discretion of the Board or any Committee to which responsibility for
administration of the Plan has been delegated pursuant to subsection 3(c), be
either Incentive Stock Options or Nonstatutory Stock Options. All Options shall
be separately designated Incentive Stock Options or Nonstatutory Stock Options
at the time of grant, and in such form as issued pursuant to Section 6.

2. DEFINITIONS

    (a) "AFFILIATE" means any parent corporation or subsidiary corporation,
whether now or hereafter existing, as those terms are defined in Sections 424(e)
and (f) respectively, of the Code.

    (b) "BOARD" means the Board of Directors of the Company.

    (c) "CODE" means the Internal Revenue Code of 1986, as amended.

    (d) "COMMITTEE" means a Committee appointed by the Board in accordance with
subsection 3(c) of the Plan.

    (e) "COMPANY" means IGEN International, Inc., a Delaware corporation,
formerly known as IGEN, Inc.

    (f) "CONSULTANT" means any Person, including an advisor, engaged by the
Company or an Affiliate to render consulting services and who is compensated for
such services, provided that the term "Consultant" shall not include Directors
who are paid only a director's fee by the Company or who are not compensated by
the Company for their services as Directors.

    (g) "CONTINUOUS STATUS AS AN EMPLOYEE OR CONSULTANT" means the employment or
relationship as a Consultant is not interrupted or terminated. The Board, in its
sole discretion, may determine whether Continuous Status as an Employee or
Consultant shall be considered interrupted in the case of: (i) any leave of
absence approved by the Board, including sick leave, military leave, or any
other personal leave; or (ii) transfers between locations of the Company or
between the Company, Affiliates or their successors.

    (h) "COVERED EMPLOYEE" means the Chief Executive Officer and the four (4)
other highest compensated officers of the Company.

    (i) "DIRECTOR" means a member of the Board.

    (j) [RESERVED]

    (k) "EMPLOYEE" means any person, including Officers and Directors, employed
by the Company or any Affiliate of the Company. Neither service as a Director
nor payment of a director's fee by the Company shall be sufficient to constitute
"employment" by the Company.

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    (l) "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended.

    (m) "FAIR MARKET VALUE" means, as of any date, the value of the common stock
of the Company determined as follows:

        (1) If the common stock is listed on any established stock exchange or a
    national market system, including without limitation the National Market
    System of the National Association of Securities Dealers, Inc. Automated
    Quotation ("NASDAQ") System, the Fair Market Value of a share of common
    stock shall be the closing sales price for such stock (or the closing bid,
    if no sales were reported) as quoted on such system or exchange (or the
    exchange with the greatest volume of trading in common stock) on the last
    market trading day prior to the day of determination, as reported in the
    Wall Street Journal or such other source as the Board deems reliable;

        (2) If the common stock is quoted on the NASDAQ System (but not on the
    National Market System thereof) or is regularly quoted by a recognized
    securities dealer but selling prices are not reported, the Fair Market Value
    of a share of common stock shall be the mean between the bid and asked
    prices for the common stock on the last market trading day prior to the day
    of determination, as reported in the Wall Street Journal or such other
    source as the Board deems reliable;

        (3) In the absence of an established market for the common stock, the
    Fair Market Value shall be determined in good faith by the Board.

    (n) "INCENTIVE STOCK OPTION" means an Option intended to qualify as an
incentive stock option within the meaning of Section 422 of the Code and the
regulations promulgated thereunder.

    (o) "NONSTATUTORY STOCK OPTION" means an Option not intended to qualify as
an Incentive Stock Option.

    (p) "OFFICER" means a person who is an officer of the Company within the
meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

    (q) "OPTION" means a stock option granted pursuant to the Plan.

    (r) "OPTION AGREEMENT" means a written agreement between the Company and an
Optionee evidencing the terms and conditions of an individual Option grant. Each
Option Agreement shall be subject to the terms and conditions of the Plan.

    (s) "OPTIONEE" means an Employee or Consultant who holds an outstanding
Option.

    (t) "OUTSIDE DIRECTOR" means a Director who either (i) is not a current
employee of the Company or an "affiliated corporation" (as defined in the
Treasury regulations promulgated under Section 162(m) of the Code), is not a
former employee of the Company or an affiliated corporation receiving
compensation for prior services (other than benefits under a tax qualified
pension plan), was not an officer of the Company or an affiliated corporation at
any time, and is not currently receiving compensation for personal services in
any capacity other than as a Director, or (ii) is otherwise considered an
"outside director" for purposes of Section 162(m) of the Code.

    (u) "PLAN" means this 1994 Stock Option Plan.

    (v) "RULE 16B-3" means Rule 16b-3 of the Exchange Act or any successor to
Rule 16b-3, as in effect when discretion is being exercised with respect to the
Plan.

3. ADMINISTRATION.

    (a) The Plan shall be administered by the Board unless and until the Board
delegates administration to a Committee, as provided in subsection 3(c).

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    (b) The Board shall have the power, subject to, and within the limitations
of, the express provisions of the Plan:

        (1) To determine from time to time which of the persons eligible under
    the Plan shall be granted Options; when and how each Option shall be
    granted; whether an Option will be an Incentive Stock Option or a
    Nonstatutory Stock Option; the provisions of each Option granted (which need
    not be identical), including the time or times such Option may be exercised
    in whole or in part; and the number of shares for which an Option shall be
    granted to each such person.

        (2) To construe and interpret the Plan and Options granted under it, and
    to establish, amend and revoke rules and regulations for its administration.
    The Board, in the exercise of this power, may correct any defect, omission
    or inconsistency in the Plan or in any Option Agreement, in a manner and to
    the extent it shall deem necessary or expedient to make the Plan fully
    effective.

        (3) To amend the Plan as provided in Section 11.

        (4) Generally, to exercise such powers and to perform such acts as the
    Board deems necessary or expedient to promote the best interests of the
    Company.

    (c) The Board may delegate administration of the Plan to a committee
composed of not fewer than two (2) members of the Board (the "Committee"). If
administration is delegated to a Committee, the Committee shall have, in
connection with the administration of the Plan, the powers theretofore possessed
by the Board (and references in this Plan to the Board shall thereafter be to
the Committee), subject, however, to such resolutions, not inconsistent with the
provisions of the Plan, as may be adopted from time to time by the Board. The
Board may abolish the Committee at any time and revest in the Board the
administration of the Plan. Notwithstanding anything in this Section 3 to the
contrary, the Board or the Committee may delegate to a committee of one or more
members of the Board the authority to grant Options to eligible persons who (1)
are not then subject to Section 16 of the Exchange Act and/or (2) are either (i)
not then Covered Employees and are not expected to be Covered Employees at the
time of recognition of income resulting from such Option, or (ii) not persons
with respect to whom the Company wishes to comply with Section 162(m) of the
Code.

4. SHARES SUBJECT TO THE PLAN.

    (a) Subject to the provisions of Section 10 relating to adjustments upon
changes in stock, the stock that may be sold pursuant to Options shall not
exceed in the aggregate One Million Seven Hundred Fifty Thousand (1,750,000)
shares of the Company's common stock. If any Option shall for any reason expire
or otherwise terminate, in whole or in part, without having been exercised in
full, the stock not purchased under such Option shall revert to and again become
available for issuance under the Plan.

    (b) The stock subject to the Plan may be unissued shares or reacquired
shares, bought on the market or otherwise.

5. ELIGIBILITY.

    (a) Incentive Stock Options may be granted only to Employees. Nonstatutory
Stock Options may be granted only to Employees and Consultants.

    (b) Reserved.

    (c) No person shall be eligible for the grant of an Incentive Stock Option
if, at the time of grant, such person owns (or is deemed to own pursuant to
Section 424(d) of the Code) stock possessing more than ten percent (10%) of the
total combined voting power of all classes of stock of the Company or of any of
its Affiliates unless the exercise price of such Incentive Stock Option is at
least one hundred ten percent (110%) of the Fair Market Value of such stock at
the date of grant and the Option is not exercisable after the expiration of five
(5) years from the date of grant.

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    (d) Subject to the provisions of Section 10 relating to adjustments upon
changes in stock, no person shall be eligible to be granted Options covering
more than two hundred thousand (200,000) shares of the Company's common stock in
any twelve (12) month period.

    (e) Notwithstanding any other provision, Outside Directors are not eligible
to be granted Options under the Plan.

6. OPTION PROVISIONS

    Each Option shall be in such form and shall contain such terms and
conditions as the Board shall deem appropriate. The provisions of separate
Options need not be identical, but each Option shall include (through
incorporation of provisions hereof by reference in the Option or otherwise) the
substance of each of the following provisions:

    (a) TERM. No Option shall be exercisable after the expiration of ten (10)
years from the date it was granted.

    (b) PRICE. The exercise price of each Incentive Stock Option shall be not
less than one hundred percent (100%) of the Fair Market Value of the stock
subject to the Option on the date the Option is granted. The exercise price of
each Nonstatutory Stock Option shall be not less than eighty-five percent (85 %)
of the Fair Market Value of the stock subject to the Option on the date the
Option is granted.

    (c) CONSIDERATION. The purchase price of stock acquired pursuant to an
Option shall be paid, to the extent permitted by applicable statutes and
regulations, either (i) in cash at the time the Option is exercised, or (ii) at
the discretion of the Board or the Committee, either at the time of the grant or
exercise of the Option, (A) by delivery to the Company of other common stock of
the Company, (B) according to a deferred payment or other arrangement (which may
include, without limiting the generality of the foregoing, the use of other
common stock of the Company) with the person to whom the Option is granted or to
whom the Option is transferred pursuant to subsection 6(d), or (C) in any other
form of legal consideration that may be acceptable to the Board.

    In the case of any deferred payment arrangement, interest shall be payable
at least annually and shall be charged at the minimum rate of interest necessary
to avoid the treatment as interest, under any applicable provisions of the Code,
of any amounts other than amounts stated to be interest under the deferred
payment arrangement.

    (d) TRANSFERABILITY. An Incentive Stock Option shall not be transferable
except by will or by the laws of descent and distribution, and shall be
exercisable during the lifetime of the person to whom the Incentive Stock Option
is granted only by such person. A Nonstatutory Stock Option shall not be
transferable except by will or by the laws of descent and distribution or
pursuant to a qualified domestic relations order satisfying the requirements of
Rule 16b-3 and the rules thereunder (a "QDRO"), and shall be exercisable during
the lifetime of the person to whom the Option is granted only by such person or
any transferee pursuant to a QDRO. The person to whom the Option is granted may,
by delivering written notice to the Company, in a form satisfactory to the
Company, designate a third party who, in the event of the death of the Optionee,
shall thereafter be entitled to exercise the Option.

    (e) VESTING. The total number of shares of stock subject to an Option may,
but need not, be allotted in periodic installments (which may, but need not, be
equal). The Option Agreement may provide that, from time to time during each of
such installment periods, the Option may become exercisable ("vest") with
respect to some or all of the shares allotted to that period, and may be
exercised with respect to some or all of the shares allotted to such period
and/or any prior period as to which the Option became vested but was not fully
exercised. The Option may be subject to such other terms and conditions on the
time or times when it may be exercised (which may be based on performance or
other criteria) as the Board may deem appropriate. The provisions of this
subsection 6(e) are subject to any Option provisions governing the minimum
number of shares as to which an Option may be exercised.

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    (f) SECURITIES LAW COMPLIANCE. The Company may require any Optionee, or any
person to whom an Option is transferred under subsection 6(d), as a condition of
exercising any such Option, (1) to give written assurances satisfactory to the
Company as to the Optionee's knowledge and experience in financial and business
matters and/or to employ a purchaser representative reasonably satisfactory to
the Company who is knowledgeable and experienced in financial and business
matters, and that he or she is capable of evaluating, alone or together with the
purchaser representative, the merits and risks of exercising the Option; and (2)
to give written assurances satisfactory to the Company stating that such person
is acquiring the stock subject to the Option for such person's own account and
not with any present intention of selling or otherwise distributing the stock.
The foregoing requirements, and any assurances given pursuant to such
requirements, shall be inoperative if (i) the issuance of the shares upon the
exercise of the Option has been registered under a then currently effective
registration statement under the Securities Act of 1933, as amended (the
"Securities Act"), or (ii) as to any particular requirement, a determination is
made by counsel for the Company that such requirement need not be met in the
circumstances under the then applicable securities laws. The Company may, upon
advice of counsel to the Company, place legends on stock certificates issued
under the Plan as such counsel deems necessary or appropriate in order to comply
with applicable securities laws, including, but not limited to, legends
restricting the transfer of the stock.

    (g) TERMINATION OF EMPLOYMENT OR RELATIONSHIP AS A CONSULTANT. In the event
an Optionee's Continuous Status as an Employee or Consultant terminates (other
than upon the Optionee's death or disability), the Optionee may exercise his or
her Option (to the extent that the Optionee was entitled to exercise it at the
date of termination) but only within such period of time ending on the earlier
of (i) the date three (3) months after the termination of the Optionee's
Continuous status as an Employee or Consultant (or such longer or shorter period
specified in the Option Agreement), or (ii) the expiration of the term of the
Option as set forth in the Option Agreement. If, after termination, the Optionee
does not exercise his or her Option within the time specified in the Option
Agreement, the Option shall terminate, and the shares covered by such Option
shall revert to and again become available for issuance under the Plan.

    (h) DISABILITY OF OPTIONEE. In the event an Optionee's Continuous Status as
an Employee or Consultant terminates as a result of the Optionee's disability,
the Optionee may exercise his or her Option (to the extent that the Optionee was
entitled to exercise it at the date of termination), but only within such period
of time ending on the earlier of (i) the date twelve (12) months following such
termination (or such longer or shorter period specified in the Option
Agreement), or (ii) the expiration of the term of the Option as set forth in the
Option Agreement. If, at the date of termination, the Optionee is not entitled
to exercise his or her entire Option, the shares covered by the unexercisable
portion of the Option shall revert to and again become available for issuance
under the Plan. If, after termination, the Optionee does not exercise his or her
Option within the time specified herein, the Option shall terminate, and the
shares covered by such Option shall revert to and again become available for
issuance under the Plan.

    (i) DEATH OF OPTIONEE. In the event of the death of an Optionee during, or
within a period specified in the Option after the termination of, the Optionee's
Continuous Status as an Employee or Consultant, the Option may be exercised (to
the extent the Optionee was entitled to exercise the Option at the date of
death) by the Optionee's estate, by a person who acquired the right to exercise
the Option by bequest or inheritance or by a person designated to exercise the
option upon the Optionee's death pursuant to subsection 6(d), but only within
the period ending on the earlier of (i) the date eighteen (18) months following
the date of death (or such longer or shorter period specified in the Option
Agreement), or (ii) the expiration of the term of such Option as set forth in
the Option Agreement. If, at the time of death, the Optionee was not entitled to
exercise his or her entire Option, the shares covered by the unexercisable
portion of the Option shall revert to and again become available for issuance
under the Plan. If, after death, the Option is not exercised within the time
specified herein, the Option shall terminate, and the shares covered by such
Option shall revert to and again become available for issuance under the Plan.

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    (j) EARLY EXERCISE. The Option may, but need not, include a provision
whereby the Optionee may elect at any time while an Employee or Consultant to
exercise the Option as to any part or all of the shares subject to the Option
prior to the full vesting of the Option. Any unvested shares so purchased may be
subject to a repurchase right in favor of the Company or to any other
restriction the Board determines to be appropriate.

    (k) WITHHOLDING. To the extent provided by the terms of an Option Agreement,
the Optionee may satisfy any federal, state or local tax withholding obligation
relating to the exercise of such Option by any of the following means or by a
combination of such means (1) tendering a cash payment; (2) authorizing the
Company to withhold shares from the shares of the common stock otherwise
issuable to the participant as a result of the exercise of the Option; or (3)
delivering to the Company owned and unencumbered shares of the common stock of
the Company.

7. COVENANTS OF THE COMPANY.

    (a) During the terms of the Options, the Company shall keep available at all
times the number of shares of stock required to satisfy such Options.

    (b) The Company shall seek to obtain from each regulatory commission or
agency having jurisdiction over the Plan such authority as may be required to
issue and sell shares of stock upon exercise of the Options; PROVIDED, HOWEVER,
that this undertaking shall not require the Company to register under the
Securities Act either the Plan, any Option or any stock issued or issuable
pursuant to any such Option. If, after reasonable efforts, the Company is unable
to obtain from any such regulatory commission or agency the authority which
counsel for the Company deems necessary for the lawful issuance and sale of
stock under the Plan, the Company shall be relieved from any liability for
failure to issue and sell stock upon exercise of such Options unless and until
such authority is obtained.

8. USE OF PROCEEDS FROM STOCK.

    Proceeds from the sale of stock pursuant to Options shall constitute general
funds of the Company.

9. MISCELLANEOUS.

    (a) The Board shall have the power to accelerate the time at which an Option
may first be exercised or the time during which an Option or any part thereof
will vest pursuant to subsection 6(e), notwithstanding the provisions in the
Option stating the time at which it may first be exercised or the time during
which it will vest.

    (b) Neither an Optionee nor any person to whom an Option is transferred
under subsection 6(d) shall be deemed to be the holder of, or to have any of the
rights of a holder with respect to, any shares subject to such Option unless and
until such person has satisfied all requirements for exercise of the Option
pursuant to its terms.

    (c) Throughout the term of any Option, the Company shall make available to
the holder of such Option, not later than one hundred twenty (120) days after
the close of each of the Company's fiscal years during the Option term, a
balance sheet and an income statement. This section shall not apply when
issuance is limited to key employees whose duties in connection with the Company
assure them access to equivalent information.

    (d) Nothing in the Plan or any instrument executed or Option granted
pursuant thereto shall confer upon any Employee, Consultant or Optionee any
right to continue in the employ of the Company or any Affiliate (or to continue
acting as a Consultant) or shall affect the right of the Company or any
Affiliate to terminate the employment or relationship as a Director or
Consultant of any Employee, Consultant or Optionee with or without cause.

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    (e) To the extent that the aggregate Fair Market Value (determined at the
time of grant) of stock with respect to which Incentive Stock Options granted
after 1986 are exercisable for the first time by any Optionee during any
calendar year under all plans of the Company and its Affiliates exceeds one
hundred thousand dollars ($100,000), the Options or portions thereof which
exceed such limit (according to the order in which they were granted) shall be
treated as Nonstatutory Stock Options.

    (f)

        (1) The Board or the Committee shall have the authority to effect, at
    any time and from time to time (i) the downward repricing of any outstanding
    Options under the Plan and/or (ii) with the consent of the affected holders
    of Options, the cancellation of any outstanding Options and the grant in
    substitution therefor of new Options under the Plan covering the same or
    different numbers of shares of Common Stock, but having an exercise price
    per share not less than eighty-five percent (85%) of the Fair Market Value
    (one hundred percent (100%) of the Fair Market Value in the case of an
    Incentive Stock Option or, in the case of a ten percent (10%) stockholder
    (as defined in subsection 5(c)), not less than one hundred and ten percent
    (110%) of the Fair Market Value) per share of Common Stock on the new grant
    date.

        (2) Shares subject to an Option canceled under this subsection 9(f)
    shall continue to be counted against the maximum award of Options permitted
    to be granted pursuant to subsection 5(d) of the Plan. The repricing of an
    Option under this subsection 9(f), resulting in a reduction of the exercise
    price, shall be deemed to be a cancellation of the original Option and the
    grant of a substitute Option; in the event of such repricing, both the
    original and the substituted Options shall be counted against the maximum
    awards of Options permitted to be granted pursuant to subsection 5(d) of the
    Plan. The provisions of this subsection 9(f) shall be applicable only to the
    extent required by Section 162(m) of the Code.

10. ADJUSTMENTS UPON CHANGES IN STOCK.

    (a) If any change is made in the stock subject to the Plan, or subject to
any Option (through merger, consolidation, reorganization, recapitalization,
stock dividend, dividend in property other than cash, stock split, liquidating
dividend, combination of shares, exchange of shares, change in corporate
structure or otherwise), the Plan will be appropriately adjusted in the
class(es) and maximum number of shares subject to the Plan pursuant to
subsection 4(a) and the maximum number of shares subject to award to any person
during any twelve (12) month period pursuant to subsection 5(d), and the
outstanding Options will be appropriately adjusted in the class(es) and number
of shares and price per share of stock subject to such outstanding Options.

    (b) In the event of: (1) a dissolution, liquidation or sale of substantially
all of the assets of the Company; (2) a merger or consolidation in which the
Company is not the surviving corporation; or (3) a reverse merger in which the
Company is the surviving corporation but the shares of the Company's common
stock outstanding immediately preceding the merger are converted by virtue of
the merger into other property, whether in the form of securities, cash or
otherwise, then to the extent permitted by applicable law: (i) any surviving
corporation shall assume any Options outstanding under the Plan or shall
substitute similar Options for those outstanding under the Plan, or (ii) such
Options shall continue in full force and effect. In the event any surviving
corporation refuses to assume or continue such Options, or to substitute similar
options for those outstanding under the Plan, then, with respect to Options held
by persons then performing services as Employees, Directors or Consultants, the
time during which such Options may be exercised shall be accelerated and the
Options terminated if not exercised prior to such event.

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11. AMENDMENT OF THE PLAN.

    (a) The Board at any time, and from time to time, may amend the Plan.
However, except as provided in Section 10 relating to adjustments upon changes
in stock, no amendment shall be effective unless approved by the stockholders of
the Company within twelve (12) months before or after the adoption of the
amendment, where the amendment will:

        (1) Increase the number of shares reserved for Options under the Plan;

        (2) Modify the requirements as to eligibility for participation in the
    Plan (to the extent such modification requires stockholder approval in order
    for the Plan to satisfy the requirements of Section 422 of the Code); or

        (3) Modify the Plan in any other way if such modification requires
    stockholder approval in order for the Plan to satisfy the requirements of
    Section 422 of the Code or to comply with the requirements of Rule 16b-3.

    (b) The Board may in its sole discretion submit any other amendment to the
Plan for stockholder approval, including, but not limited to, amendments to the
Plan intended to satisfy the requirements of Section 162(m) of the Code and the
regulations promulgated thereunder regarding the exclusion of performance-based
compensation from the limit on corporate deductibility of compensation paid to
certain executive officers.

    (c) It is expressly contemplated that the Board may amend the Plan in any
respect the Board deems necessary or advisable to provide Optionees with the
maximum benefits provided or to be provided under the provisions of the Code and
the regulations promulgated thereunder relating to Incentive Stock Options
and/or to bring the Plan and/or Incentive Stock Options granted under it into
compliance therewith.

    (d) Rights and obligations under any Option granted before amendment of the
Plan shall not be altered or impaired by any amendment of the Plan unless (i)
the Company requests the consent of the person to whom the Option was granted
and (ii) such person consents in writing.

12. TERMINATION OR SUSPENSION OF THE PLAN.

    (a) The Board may suspend or terminate the Plan at any time. Unless sooner
terminated, the Plan shall terminate on July 10, 2004, which shall be within ten
(10) years from the date the Plan is adopted by the Board or approved by the
stockholders of the Company, whichever is earlier. No Options may be granted
under the Plan while the Plan is suspended or after it is terminated.

    (b) Rights and obligations under any Option granted while the Plan is in
effect shall not be impaired (or, for grants before July 24, 1998, altered) by
suspension or termination of the Plan, except with the consent of the person to
whom the Option was granted.

13. EFFECTIVE DATE OF PLAN.

    The Plan shall become effective as determined by the Board, but no Options
granted under the Plan shall be exercised unless and until the Plan has been
approved by the stockholders of the Company, which approval shall be within
twelve (12) months before or after the date of the Plan is adopted by the Board,
and, if required, an appropriate permit has been issued by the Commissioner of
Corporations of the State of California.

                                       8<PAGE>

                                  EXHIBIT 10.23

                      AMENDED AND RESTATED PROMISSORY NOTE
            (for acquisition of IGEN International, Inc. Common Stock
                       under the 1994 Stock Option Plan)
                          Effective as of July 22, 2000
                             Gaithersburg, Maryland

WHEREAS, on July 22, 2000, IGEN International, Inc. ("IGEN" or the "LENDER")
made a loan in the sum of Two million and Sixty thousand and Five hundred
dollars ($2,060,500.00) (the "LOAN") to the undersigned (the "Borrower")
pursuant to the authority granted by a resolution of the Board of Directors of
the Lender in July 2000 (the "RESOLUTION"); and

WHEREAS, the Lender and the Borrower now wish to amend the promissory note
evidencing the Loan to correct the terms of the Loan to make the terms
consistent with the Borrower's and the Lender's intention and with the
Resolution.

FOR VALUE RECEIVED, the undersigned (the "BORROWER") promises to pay to the
order of IGEN International, Inc., ("IGEN" or the "LENDER") the sum of Two
million and Sixty thousand and Five hundred dollars ($2,060,500.00), together
with interest thereon as set forth below, at 16020 Industrial Drive,
Gaithersburg, Maryland 20877, or at such other place as the Lender may designate
without offset. This instrument is referred to as the "NOTE."

A.   SPECIFIC TERMS

     1.  INTEREST:  From the date hereof until repayment, interest shall accrue
     hereunder at a rate of 6.62% per annum and will compound and be payable
     annually. Interest payable hereunder shall be calculated for the actual
     days elapsed on the basis of a 365-day year.

     2.  PAYMENTS:  The entire principal amount and any accrued and unpaid
     interest shall become due and payable on July 22, 2007 or as accelerated
     under Section A(3) or B(3) below, whichever occurs first.

     3.  ACCELERATION:  This Note will become due and payable not later than
     the thirtieth (30th) day after the Borrower's employment with IGEN ceases
     for any reason.

     4. SECURITY: To secure payment of this Note, the Borrower has transferred,
     pledged and granted a first priority security interest in, and delivered to
     the Lender his certificates for, one hundred thousand (100,000) shares of
     IGEN Common Stock (the "COLLATERAL"). The fair market value of the
     Collateral at least equals the amount borrowed under this Note on the date
     it was signed.

B.   GENERAL CONDITIONS

     1. The Lender shall apply all of the Borrower's payments and prepayments
     first to any accrued and unpaid interest and then to the unpaid principal
     balance of this Note. Payment by the Borrower of any amount due under this
     Note shall consist of delivery to the Lender of either cash, bank cashier's
     or certified check payable to the Lender without endorsement. Payment of
     principal or interest may be made prior to the date upon which it is due
     without penalty.

     2. Upon the occurrence of any one or more of the Events of Default set
     forth under Section B(3) below, the entire unpaid principal balance of this
     Note, together with all accrued and unpaid interest hereunder, shall, at
     the Lender's option, become immediately due and payable without notice of
     demand of any kind.

<PAGE>

     3.  An "EVENT OF DEFAULT" shall mean the occurrence of any one or more of
     the following events:

         (a) the failure by the Borrower to pay when due any amount due
             hereunder;

         (b) if the Borrower shall become insolvent or shall generally not pay
             his debts as they become due, or shall file a voluntary petition
             under any Federal insolvency legislation (the "BANKRUPTCY ACT")
             seeking liquidation, reorganization or to effect a plan or other
             arrangement with creditors, or shall be unable, or shall admit in
             writing his or her inability to pay his debts as they become due,
             or shall file an answer admitting the jurisdiction of the
             Bankruptcy Court and the material allegations of any involuntary
             petition filed pursuant to the Bankruptcy Act, or an order for
             relief under the Bankruptcy Act shall be entered, or if the
             Borrower shall make an assignment or arrangement or enter into a
             trust indenture for the benefit of its creditors, or shall apply
             for, consent to, or suffer the appointment of any receiver or
             trustee for any of his property; or

         (c) if any lien, writ of attachment or execution or any similar process
             is imposed, issued or levied against the Collateral or all or a
             substantial part of Borrower's other property, which judgment,
             lien, writ or process is not discharged, released, stayed, bonded
             or vacated within fifteen (15) days after its entry, imposition,
             issue or levy.

     4. In an Event of Default, the Lender shall have the right to proceed to
     collect the indebtedness due under this Note by action or proceeding
     against the Collateral or against the Borrower or against both the
     Collateral and the Borrower, without first having to exhaust its remedies
     against any other collateral or party, and such action or proceeding shall
     not be construed as a waiver of any other rights or powers to proceed
     thereafter against any other collateral or party. In an Event of Default,
     the Lender shall have all rights in the Collateral provided by the Uniform
     Commercial Code.

     5. No delay or omission by the Lender in exercising or enforcing any of its
     powers, rights, privileges, remedies, or discretions hereunder shall
     operate as a bar thereto on that occasion or on any other occasion. No
     waiver of any default hereunder or as otherwise provided by law shall
     operate as a waiver of or bar to any other default hereunder, or as a
     continuing waiver.

     6. The Borrower shall pay all costs and expenses, including, without
     limitation, reasonable attorney's and expert's fees, expenses and
     disbursements, in connection with the protection or enforcement of any of
     the Lender's rights against the Borrower and against or with respect to the
     Collateral, whether or not suit is instituted by or against the Lender.

     7. The Borrower hereby waives presentment, demand, notice of maturity,
     dishonor, protest and notice of protest, and also waives any delay on the
     part of the Lender. The Borrower assents to any extension or other
     indulgence (including, without limitation, the release or substitution of
     collateral) permitted by the Lender with respect to this Note and the
     Collateral.

     8. This Note shall be binding upon the Borrower and the Borrower's
     respective heirs, executors, administrators, successors, assigns and
     representatives, and shall inure to the benefit of the Lender and its
     successors, endorsees and assigns.

     9.  The captions in this Note are for convenience only and do not
     constitute part of this instrument.

     10. The Borrower represents and warrants to the Lender that he or she has
     the full power and authority to execute the Note and that this Note
     constitutes a valid, binding and enforceable obligation of the Borrower.

<PAGE>

     11. Upon any transfer or assignment of this Note by the Lender, the
     Collateral held under this Note at the time of transfer or assignment may
     be delivered to the assignee or transferee, who shall thereupon become
     vested with all the rights and powers given to the Lender herein.

     12. This Note shall be governed by the laws of the State of Maryland,
     excluding its conflicts of laws, principles, and courts sitting in the
     State of Maryland shall provide the exclusive forum for the resolution of
     any disputes hereunder.

WITNESS the following signatures.

                                           /s/ SAMUEL J. WOHLSTADTER
                                           -------------------------
                                           Signature of Borrower

                                           Printed Name and Address of Borrower:

                                           SAMUEL J. WOHLSTADTER
                                           -------------------------------------
                                           16020 INDUSTRIAL DRIVE
-----------------------------------        -------------------------------------
                                           GAITHERSBURG, MD  20877
                                           -------------------------------------

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