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                        GENAISSANCE PHARMACEUTICALS, INC.

                        EMPLOYEE STOCK PURCHASE PLAN 2000


1.       PURPOSE.

         This Employee Stock Purchase Plan 2000 (the "Plan") is adopted by
Genaissance Pharmaceuticals, Inc. (the "Company") to provide Eligible Employees
who wish to become shareholders of the Company an opportunity to purchase shares
of Common Stock, par value $0.01 per share, of the Company ("Common Stock"). The
Plan is intended to qualify as an "employee stock purchase plan" under Section
423 of the Internal Revenue Code of 1986, as amended (the "Code"), and the
provisions of the Plan shall be construed so as to extend and limit
participation in a manner consistent with the requirements of Section 423;
provided that, if and to the extent authorized by the Board, the fact that the
Plan does not comply in all respects with the requirements of Section 423 shall
not affect the operation of the Plan or the rights of Employees hereunder.

2.       CERTAIN DEFINITIONS.

         As used in this Plan:

         (a) "Board" means the Board of Directors of the Company, and
"Committee" means the Compensation Committee of the Board or such other
committee as the Board may appoint from time to time to administer the Plan.

         (b) "Coordinator" means the officer of the Company or other person
charged with day-to-day supervision of the Plan as appointed from time to time
by the Board or the Committee.

         (c) "Designated Beneficiary" means a person designated by an Employee
in the manner prescribed by the Committee or the Coordinator to receive certain
benefits provided in this Plan in the event of the death of the Employee.

         (d) "Eligible Employee" with respect to any Offering hereunder means
any Employee who, as of the Offering Commencement Date for such Offering:

             (i) has been a Full-time Employee of the Company or any of its
Subsidiaries for not less than 90 days; and

             (ii) would not, immediately after any right to acquire Shares in
such Offering is granted, own stock or rights to purchase stock possessing five
percent (5%) or more of the total combined voting power or value of all classes
of stock of the Company or of any subsidiary corporation, determined in
accordance with Section 423.

         (e) "Employee" means an employee (as that term is used in Section 423)
of the Company or any of its Subsidiaries.
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         (f) "Fair Market Value" of a Share shall mean the fair market value of
a share of Common Stock, as determined by the Committee.

         (g) "Full-time Employee" is an Employee whose customary employment is
for more than (i) 20 hours per week and (ii) five months, in the calendar year
during which the respective Offering Commencement Date occurs.

         (h) "Offering" is an offering of Shares pursuant to Section 5 of the
Plan.

         (i) "Offering Commencement Date" means the date on which an Offering
under the Plan commences, and "Offering Termination Date" means the date on
which an Offering under the Plan terminates.

         (j) "Purchase Date" means each date on which the rights granted under
the Plan may be exercised for the purchase of Shares.

         (k) "Section 423" and subdivisions thereof refer to Section 423 of the
Code or any successor provision(s).

         (l) "Shares" means the shares of Common Stock issuable under the Plan.

         (m) "Subsidiary" means a subsidiary corporation, as defined in Section
424 of the Code, of the Company the Employees of which are designated by the
Board of Directors or the Committee as eligible to participate in the Plan.

3. ADMINISTRATION OF THE PLAN.

         The Committee shall administer, interpret and apply all provisions of
the Plan as it deems necessary or appropriate, subject, however, at all times to
the final jurisdiction of the Board of Directors. The Board may in any instance
perform any of the functions of the Committee hereunder. The Committee may
delegate administrative responsibilities to the Coordinator, who shall, for
matters involving the Plan, be an ex officio member of the Committee.
Determinations made by the Committee and approved by the Board of Directors with
respect to any provision of the Plan or matter arising in connection therewith
shall be final, conclusive and binding upon the Company and upon all
participants, their heirs or legal representatives.

4.       SHARES SUBJECT TO THE PLAN.

         The maximum aggregate number of Shares that may be purchased upon
exercise of rights granted under the Plan shall be 250,000. Appropriate
adjustments in such amount, the number of Shares covered by outstanding rights
granted hereunder, the securities that may be purchased hereunder, the Exercise
Price, and the maximum number of Shares or other securities that an employee may
purchase (pursuant to Section 8 below) shall be made to give effect to any
mergers, consolidations, reorganizations, recapitalizations, stock splits, stock
dividends or other relevant changes in the capitalization of the Company
occurring after the effective date of the Plan; provided that any fractional
Share otherwise issuable hereunder as a result of such an adjustment shall be
adjusted downward to the nearest full Share. Any agreement of merger or
consolidation involving the Company will include appropriate provisions for
protection of the


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then existing rights of participating employees under the Plan. Either
authorized and unissued Shares or treasury Shares may be purchased under the
Plan. If for any reason any right under the Plan terminates in whole or in part,
Shares subject to such terminated right may again be subjected to a right under
the Plan.

5.       OFFERINGS; PARTICIPATION.

         (a) From time to time, the Company, by action of the Committee, will
grant rights to purchase Shares to Eligible Employees pursuant to one or more
Offerings, each having an Offering Commencement Date, an Offering Termination
Date, and one or more Purchase Dates as designated by the Committee. No Offering
may last longer than twenty-seven (27) months or such longer period as may then
be consistent with Section 423. The Committee may limit the number of Shares
issuable in any Offering, either before or during such Offering.

         (b) Participation in each Offering shall be limited to Eligible
Employees who elect to participate in such Offering in the manner, and within
the time limitations, established by the Committee. No person otherwise eligible
to participate in any Offering under the Plan shall be entitled to participate
if he or she has elected not to participate. Any such election not to
participate may be revoked only with the consent of the Committee.

         (c) An Employee who has elected to participate in an Offering may make
such changes in the level of payroll deductions as the Committee may permit from
time to time, or may withdraw from such Offering, by giving written notice to
the Company before any Purchase Date. No Employee who has withdrawn from
participating in an Offering may resume participation in the same Offering, but
he or she may participate in any subsequent Offering if otherwise eligible.

         (d) Upon termination of a participating Employee's employment for any
reason, including retirement but excluding death or disability (as defined in
Section 22(e)(3) of the Code) while in the employ of the Company or a
Subsidiary, such Employee will be deemed to have withdrawn from participation in
all pending Offerings.

         (e) Upon termination of a participating Employee's employment because
of disability or death, the Employee or his or her Designated Beneficiary, if
any, as the case may be, shall have the right to elect, with respect to each
Offering in which the Employee was then participating, by written notice given
to the Coordinator within 30 days after the date of termination of employment
(but not later than the next applicable Purchase Date for each Offering), either
(i) to withdraw from such Offering or (ii) to exercise the Employee's right to
purchase Shares on the next Purchase Date of such Offering to the extent of the
accumulated payroll deductions or other contributions in the Employee's account
at the date of termination of employment. If no such election with respect to
any Offering is made within such period, the Employee shall be deemed to have
withdrawn from such Offering on the date of termination of employment. The
foregoing election is not available to any person, such as a legal
representative, as such, other than the Employee or a Designated Beneficiary.


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6.       EXERCISE PRICE.

         The rights granted under the Plan shall be exercised and Shares shall
be purchased at a price per Share (the "Exercise Price") determined by the
Committee from time to time; provided that the Exercise Price shall not be less
than eighty-five percent (85%) of the Fair Market Value of a Share on (a) the
respective Offering Commencement Date or (b) the respective Purchase Date,
whichever is lower.

7.       EXERCISE OF RIGHTS; METHOD OF PAYMENT.

         (a) Participating Employees may pay for Shares purchased upon exercise
of rights granted hereunder through regular payroll deductions, by lump sum cash
payment, by delivery of shares of Common Stock valued at Fair Market Value on
the date of delivery, or a combination thereof, as determined by the Committee
from time to time. No interest shall be paid upon payroll deductions or other
amounts held hereunder (whether or not used to purchase Shares) unless
specifically provided for by the Committee. All payroll deductions and other
amounts received or held by the Company under this Plan may be used by the
Company for any corporate purpose, and the Company shall not be obligated to
segregate such amounts.

         (b) Subject to any applicable limitation on purchases under the Plan,
and unless the Employee has previously withdrawn from the respective Offering,
rights granted to a participating Employee under the Plan will be exercised
automatically on the Purchase Date of the respective Offering coinciding with
the Offering Termination Date, and the Committee may provide that such rights
may at the election of the Employee be exercised on one or more other Purchase
Dates designated by the Committee within the period of the Offering, for the
purchase of the number of whole Shares that may be purchased at the applicable
Exercise Price with the accumulated payroll deductions or other amounts
contributed by such Employee as of the respective Purchase Date. Fractional
Shares will not be issued under the Plan, and any amount that would otherwise
have been applied to the purchase of a fractional Share shall be retained and
applied to the purchase of Shares in the following Offering unless the
respective Employee elects otherwise. The Company will deliver to each
participating Employee a certificate representing the shares of Common Stock
purchased within a reasonable time after the Purchase Date.

         (c) Any amounts contributed by an Employee or withheld from the
Employee's compensation that are not used for the purchase of Shares, whether
because of such Employee's withdrawal from participation in an Offering
(voluntarily, upon termination of employment, or otherwise) or for any other
reason, except as provided in Section 7(b), shall be repaid to the Employee or
his or her Designated Beneficiary or legal representative, as applicable, within
a reasonable time thereafter.

         (d) The Company's obligation to offer, sell and deliver Shares under
the Plan at any time is subject to (i) the approval of any governmental
authority required in connection with the authorized issuance or sale of such
Shares, (ii) satisfaction of the listing requirements of any national securities
exchange or securities market on which the Common Stock is then listed, and
(iii) compliance, in the opinion of the Company's counsel, with all applicable
federal and state securities and other laws.


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8.       LIMITATIONS ON PURCHASE RIGHTS.

         (a) Any provision of the Plan or any other employee stock purchase plan
of the Company or any subsidiary (collectively, "Other Plans") to the contrary
notwithstanding, no Employee shall be granted the right to purchase Common Stock
(or other stock of the Company and any subsidiary) under the Plan and all Other
Plans at a rate that exceeds an aggregate of $25,000 (or such other maximum as
may be prescribed from time to time by Section 423) in Fair Market Value of such
stock (determined at the time the rights are granted) for each calendar year in
which any such right is outstanding.

         (b) An Employee's participation in any one or a combination of
Offerings under the Plan shall not exceed such additional limits as the
Committee may from time to time impose.

9.       TAX WITHHOLDING.

         Each participating Employee shall pay to the Company or the applicable
Subsidiary, or make provision satisfactory to the Committee for payment of, any
taxes required by law to be withheld in respect of the purchase or disposition
of Shares no later than the date of the event creating the tax liability. In the
Committee's discretion and subject to applicable law, such tax obligations may
be paid in whole or in part by delivery of Shares to the Company, including
Shares purchased under the Plan, valued at Fair Market Value on the date of
delivery. The Company or the applicable Subsidiary may, to the extent permitted
by law, deduct any such tax obligations from any payment of any kind otherwise
due to the Employee or withhold Shares purchased hereunder, which shall be
valued at Fair Market Value on the date of withholding.

10. PARTICIPANTS' RIGHTS AS SHAREHOLDERS AND EMPLOYEES.

         (a) No participating Employee shall have any rights as a shareholder in
the Shares covered by a right granted hereunder until such right has been
exercised, full payment has been made for such Shares, and the Share certificate
is actually issued.

         (b) Each Employee is an employee-at-will (that is to say that either
the Employee or the Company or any Subsidiary may terminate the employment
relationship at any time for any reason or no reason at all) unless and only to
the extent provided in a written employment agreement for a specified term
executed by the chief executive officer of the Company or his duly authorized
designee or the authorized signatory of any Subsidiary. Neither the adoption,
maintenance, nor operation of the Plan nor any grant of rights hereunder shall
confer upon any Employee any right with respect to the continuance of his/her
employment with the Company or any Subsidiary nor shall they interfere with the
rights of the Company or Subsidiary to terminate any Employee at any time or
otherwise change the terms of employment, including, without limitation, the
right to promote, demote or otherwise re-assign any Employee from one position
to another within the Company or any Subsidiary.


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11.      RIGHTS NOT TRANSFERABLE.

         Rights under the Plan are not assignable or transferable by a
participating Employee other than by will or the laws of descent and
distribution and, during the Employee's lifetime, are exercisable only by the
Employee. The Company may treat any attempted INTER VIVOS assignment as an
election to withdraw from all pending Offerings.

12.      AMENDMENTS TO OR TERMINATION OF THE PLAN.

         The Board shall have the right to amend, modify or terminate the Plan
at any time without notice, subject to any stockholder approval that the Board
determines to be necessary or advisable; provided that the rights of Employees
hereunder with respect to any ongoing or completed Offering shall not be
adversely affected.

13.      GOVERNING LAW.

         Subject to overriding federal law, the Plan shall be governed by and
interpreted consistently with the laws of the State of Delaware.

14.      EFFECTIVE DATE AND TERM.

         This Plan will become effective on April 18, 2000, and no rights
shall be granted hereunder after April 18, 2010.

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