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                                                                    EXHIBIT 10.1


                      PRAECIS PHARMACEUTICALS INCORPORATED
                          EMPLOYEE STOCK PURCHASE PLAN


         PRAECIS PHARMACEUTICALS INCORPORATED, a Delaware corporation (the
"Company"), establishes this Employee Stock Purchase Plan (the "Plan") so that
Eligible Employees (as defined herein), if any, may be granted options to
purchase Common Stock, par value $.01 per share, of the Company ("Common
Stock").

1.      PURPOSE.

         The Plan provides Eligible Employees an opportunity to acquire shares
of Common Stock under circumstances which enable them to obtain the income tax
benefits described in Section 423 of the Internal Revenue Code of 1986, as
amended (the "Code"). The Plan is intended to provide employees an incentive to
continue to promote the Company's best interests and to enhance its long-term
performance.

2.      DEFINITIONS.

         Wherever used, the following words and phrases will have the meanings
stated below unless a different meaning is plainly required by the context:

"Affiliated Company" means any subsidiary corporation of the Company, as defined
in Section 424(f) of the Code.

"Applicable Grant Date" means for any Option the date on which such Option was
granted, which shall be a Semiannual Grant Date.

"Board" means the Board of Directors of the Company.

"Committee" means a committee appointed by the Board to which the Board may (but
shall not be required to) delegate its powers to administer the Plan.

"Compensation" means the total cash remuneration a Participant receives during
an Exercise Period as salary or wages, including overtime pay and bonuses and
excluding all other forms of remuneration.

"Disability" means permanent and total disability as defined in Section 22(e)(3)
of the Code.


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"Effective Date" means July 3, 2000.

"Eligible Employee" means each person who, on an applicable Semiannual Grant
Date, is employed by the Company or an Affiliated Company and has been an
employee for six (6) or more months at that date. An employee will not be
eligible to participate during an Exercise Period if his or her customary
employment as of the first day of the period is either (i) less than 20 hours
per week or (ii) 5 months or less on a calendar year basis. No employee will be
eligible if he or she is on an applicable Semiannual Grant Date an owner of 5%
or more of the outstanding capital stock of the Company or an Affiliated
Company, as determined under Section 424(d) of the Code.

"Exercise Date" means any date on which an Eligible Employee purchases Common
Stock pursuant to an Option under the Plan, which shall, with respect to each
Option, be the last day of the Exercise Period in which such Option is granted.

"Exercise Period" means the approximate six-month period commencing on each of
July 3, 2000, January 1, 2001, July 2, 2001 and December 31, 2001 and ending at
5 p.m. (Boston time) on each of December 31, 2000, July 1, 2001, December 30,
2001 and June 30, 2002, respectively. If the Plan is terminated, then the
Exercise Period in which it is terminated shall end on the date immediately
preceding the effective date of such termination.

"Fair Market Value Per Share of Common Stock" on the day of determination shall
mean the last sale price per share of Common Stock on such day reported on the
Nasdaq National Market as published in The Wall Street Journal or, if no such
sale is so reported, the average of the reported closing bid and asked prices on
such day in the over-the-counter market, as furnished by the National
Association of Securities Dealers Automated Quotation System, or, if such price
at the time is not available from such system, as furnished by any similar
system then engaged in the business of reporting such prices and selected by the
Board or, if there is no such system, as furnished by any member of the National
Association of Securities Dealers, selected by the Board. If the Common Stock is
neither reported on the Nasdaq National Market nor traded on the
over-the-counter market, fair market value shall be such value as the Board, in
good faith, determines. Notwithstanding any provision of the Plan to the
contrary, no determination made with respect to the Fair Market Value Per Share
of Common Stock subject to an Option shall be inconsistent with Section 423 of
the Code.

"Initial Notice Period" means the period beginning on the Effective Date and
ending on the 15th day thereafter.


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"Notice Period" means that period beginning 30 days prior to the applicable
Semiannual Grant Date (other than the first Semiannual Grant Date) and ending
on the 15th day prior to said date.

"Option" means an option granted hereunder which will entitle an Eligible
Employee to purchase shares of Common Stock.

"Option Price" means the lower of: (1) 85% of the Fair Market Value Per Share of
Common Stock as of the Applicable Grant Date on which the Option being exercised
was granted or (2) 85% of the Fair Market Value Per Share of Common Stock as of
the Exercise Date on which such Option is exercised.

"Participant" means an Eligible Employee who has elected to participate in the
Plan during the period between such election and the termination of such
Eligible Employee's participation in the Plan.

"Retirement" means a termination of a Participant's employment with the Company
on or after the first day of the month of a Participant's 65th birthday.

"Semiannual Grant Date" means each of July 3, 2000, January 1, 2001, July 2,
2001 and December 31, 2001.

"Withholding Account" means a bookkeeping record of all amounts withheld during
an Exercise Period for a specific Eligible Employee, which are available for the
exercise of an Option granted hereunder. Specific segregation of funds is not
required.

3.       ADMINISTRATION.

         The Plan shall be administered by the Board, which, to the extent it
shall determine, may delegate its powers with respect to the administration of
the Plan (except its powers to terminate or amend the Plan) to the Committee. If
the Board chooses to appoint a Committee, references hereinafter to the Board
shall be deemed to refer to the Committee. Subject to the express provisions of
the Plan, the Board may interpret the Plan, prescribe, amend and rescind rules
and regulations relating to it, determine the terms and provisions of the
Options granted hereunder and make all other determinations necessary or
advisable for the administration of the Plan; provided, however, that all such
interpretations, rules, determinations, terms and conditions shall be made and
prescribed in the context of preserving the tax treatment of the Options under
this Plan granted to Eligible Employees subject to United States federal income
taxation and preserving the tax treatment of the Plan itself under Section 423
of the Code. The determinations of the Board on all matters regarding the Plan
shall be conclusive.


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4.       MAXIMUM SHARES TO BE GRANTED UNDER THE PLAN.

         The aggregate number of shares of Common Stock available for issuance
upon the exercise of Options granted pursuant to Section 5 shall be Forty
Thousand (40,000) as of July 3, 2000, with an additional Forty Thousand
(40,000) shares available as of each of January 1, 2001, July 2, 2001 and
December 31, 2001, subject to adjustment as set forth below or pursuant to
Section 9. Shares of Common Stock delivered pursuant to the Plan will be
authorized but unissued shares or treasury shares. In the event that any Option
granted pursuant to Section 5 expires or is terminated, surrendered or cancelled
without being exercised, in whole or in part, for any reason, the number of
shares of Common Stock theretofore subject to such Option shall again be
available as shares underlying Options which may be granted for grant at the
next Semiannual Grant Date pursuant to Section 5 and shall increase the
aggregate number of shares of Common Stock underlying Options available for
grant during the succeeding Exercise Period.

5.       ELIGIBILITY FOR PARTICIPATION AND GRANTING OF OPTIONS.

         (a) Each employee of the Company who enrolls in the Plan and who is an
Eligible Employee on an applicable Semiannual Grant Date is granted without any
further action by the Board an Option hereunder which will entitle him or her to
purchase, on the immediately following Exercise Date at the Option Price per
share for Options granted on such date, shares of Common Stock equal in value up
to ten percent (10%) of the Eligible Employee's Compensation during the Exercise
Period divided by such applicable Option Price per share of Common Stock.

         (b) If the number of shares of Common Stock for which Options are
granted pursuant to Section 5(a) exceeds the applicable number provided for in
Section 4, then the Options granted under Section 5(a) to all Eligible Employees
shall, in a nondiscriminatory manner, be reduced on a pro rata basis in a manner
which the Board determines to be consistent with Section 423 of the Code.

         (c) No Eligible Employee shall be granted an Option under the Plan
which permits his or her rights to purchase stock under all employee stock
purchase plans (as defined in Section 423 of the Code) of the Company and any
Affiliated Company to accrue at a rate which exceeds $25,000 of fair market
value of such stock (determined at the time of the grant of such Option) for
each calendar year in which such Option is outstanding at any time. Any Option
granted under the Plan shall be deemed to be modified to the extent necessary to
satisfy this Section 5(c).


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6.       TERMS OF OPTIONS.

         (a) Each Option shall automatically be exercised on the last day of the
Exercise Period for such Option, using the funds which have accrued in a
Participant's Withholding Account as of such day, unless the Participant
withdraws from the Plan or is deemed to withdraw during the Exercise Period. An
Option granted hereunder may be exercised only through the use of the funds
which have accrued in a Participant's Withholding Account. Any Option, to the
extent unexercised on the Exercise Date, shall expire on the Exercise Date.

         (b) As soon as reasonably possible following exercise in accordance
with Section 6(a) and upon the Participant's written request, a certificate
representing the whole number of shares of Common Stock purchased, registered in
the name of the Participant, shall be delivered to the Participant or to such
other person designated by the Participant, including, without limitation, the
Participant's broker.

         (c) A Participant shall be deemed to have withdrawn from participation
in the Plan upon the occurrence of any of the following events:

                  (i) VOLUNTARY DISCONTINUANCE WHILE EMPLOYED. A Participant
may discontinue his or her election and withdraw from the Plan by giving written
notice to the Company no later than the last day of the Notice Period within
that Exercise Period, specifying that the Participant is so withdrawing from the
Plan; provided, however, that a Participant who shall have discontinued his or
her election to participate and withdrawn from the Plan may not participate in
the Plan during the next following Exercise Period.

                  (ii) TERMINATION OF EMPLOYMENT. Unless employment has
terminated due to Retirement, Disability or death, a Participant will be deemed
to have discontinued participation on the first day of the Exercise Period in
which such Participant's termination of employment occurs and amounts withheld
from compensation during the Exercise Period will be refunded.

                  (iii) RETIREMENT. In the event a Participant's employment
terminates because of Retirement during the first three months of an Exercise
Period, the Participant will be deemed to have discontinued participation on the
first day of the Exercise Period in which Retirement occurs and amounts withheld
from Compensation during the Exercise Period will be refunded. If Retirement
occurs during the last three months of the Exercise Period, the Participant will
continue to participate through the balance of the Exercise Period in which
Retirement occurs (without further withholding) unless he or she elects a
voluntary discontinuance within the Notice Period for that Exercise Period.


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                  (iv) DEATH OR DISABILITY. In the event the employment of the
Participant by the Company or an Affiliated Company terminates as a result of
the Participant's Disability or death, the Participant will be deemed to
participate (without further withholding) through the balance of the Exercise
Period in which death or Disability occurs, unless he or she (or the executor,
administrator or representative, as the case may be) elects a voluntary
discontinuance within the Notice Period for that Exercise Period.

                  (v) LEVY OR ATTACHMENT. The filing with or levying upon the
Company or the custodian of any judgment, attachment, garnishee or other court
order affecting the Participant's account under the Plan will automatically
terminate such Participant's participation in the Plan and amounts withheld from
compensation during the Exercise Period will be refunded.

                  (vi) PLAN TERMINATION/EXPIRATION. Subject to Section 12(b),
termination of the Plan will terminate the participation of all Participants in
the Plan.

         (d) A Participant's employment shall not be deemed terminated by reason
of a transfer to another employer which is related to the Company within the
meaning of Sections 424(e) or (f) of the Code. A Participant who has elected
participation under the Plan who is absent from work with the Company or with an
Affiliated Company because of temporary disability (any disability other than a
permanent and total Disability) or who is on leave of absence for a period of
less than 90 days shall not, during the period of any such absence, be deemed,
by virtue of such absence alone, to have terminated employment. In the case of a
leave of absence which is longer than 90 days, a Participant will not be deemed
to have terminated employment until the later of the 91st day of such leave or,
if later, such date as the Participant's reemployment rights are not protected
by contract or law.

         (e) Upon the discontinuance of an election and withdrawal from the Plan
by a Participant, all withheld amounts in such Participant Withholding Account
shall be transferred to such Participant within thirty (30) days of such
discontinuance and withdrawal, except to the extent such withheld amounts are
applied to the exercise of an Option as provided above. In no event shall any
amounts be withheld from a Participant's Compensation for allocation to such
Participant's Withholding Account after the date such Participant's employment
shall cease.

         (f) In no event may any discontinuance of a Participant's election and
withdrawal from the Plan be in respect to a portion rather than all of such
Participant's Withholding Account on such date.


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7.       PAYMENT FOR COMMON STOCK THROUGH WITHHOLDING.

         (a)  EMPLOYEE CONTRIBUTIONS

         Each Eligible Employee may elect to participate in the Plan by filing
an enrollment application and payroll withholding form with his or her
employer's payroll department during the Initial Notice Period or during a
Notice Period, which election shall be effective in the case of an election
filed during the Initial Notice Period, for the Exercise Period commencing on
the Effective Date and all subsequent Exercise Periods, or, in the case of an
election filed during a Notice Period, for the next Exercise Period and for all
subsequent Exercise Periods, until, in any case, such Participant's
participation in the Plan terminates. Each Eligible Employee who elects to
participate shall specify the amount of his or her contributions to be made by
payroll deduction by specifying a whole percentage from 1% to 10% of such
Participant's Compensation payable for each payroll period.

         No interest shall accrue or be payable to any Participant in the Plan
with respect to any sums withheld at the Participant's election, whether such
sums be applied to purchase Common Stock, or are returned to the Participant.

         Payroll deductions may be increased by a Participant only during a
subsequent Notice Period, but may be decreased, upon the Participant's written
election, effective as of the first payroll period for which it is
administratively practical to put the decrease into effect.

         (b)  APPLICATION OF PAYROLL CONTRIBUTIONS

         The Company shall maintain a separate account into which it shall
deposit all amounts withheld for payment of shares of Common Stock and shall
maintain sufficient records reflecting each Participant's Withholding Account.

         On the last day of each Exercise Period all amounts in a Participant's
With holding Account shall be paid over to the Company in payment of the Option
Price for the number of whole shares of Common Stock which can be purchased on
such date with such withheld total amount, unless otherwise directed in
accordance with Section 6 above. In lieu of fractional shares, unapplied cash
shall be carried forward to the next Exercise Period unless the Participant
requests a cash payment.

8.       TRANSFERABILITY OF OPTIONS AND COMMON STOCK.

         (a) No Option may be transferred, assigned, pledged or hypothecated
(whether by operation of law or otherwise), except as provided by will or the
applicable laws of descent or distribution, and no Option shall be subject to
execu-


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tion, attachment or similar process. Any attempted assignment, transfer, pledge,
hypothecation or other disposition of an Option, or levy of attachment or
similar process upon the Option not specifically permitted herein shall be null
and void and without effect. An Option may be exercised only by the Eligible
Employee during his or her lifetime, or by his or her legal representative if
permitted by Section 423 of the Code, or pursuant to Section 6 by his or her
estate or the person who acquires the right to exercise such Option upon his or
her death by bequest or inheritance.

         (b) Participants in the Plan who wish to avail themselves of the
favorable tax benefits of Section 423 of the Code may not transfer or otherwise
dispose of shares of Common Stock acquired by them or on their behalf under the
Plan (other than in the case of a Participant's death) until after the later of
one year from the date of acquisition of said shares and two years after the
Applicable Grant Date of the Option pursuant to which said shares of Common
Stock were acquired.

         (c) Each Eligible Employee who receives shares of Common Stock pursuant
to the Plan agrees, by electing to participate, to notify the Company, in
writing, immediately after such Participant makes a Disqualifying Disposition of
any shares acquired pursuant to the exercise of an Option under the Plan. A
Disqualifying Disposition is any disposition (including any sale) of such shares
before the later of two years after the Applicable Grant Date for said Option or
one year after the receipt of shares pursuant to the exercise of said Option. If
the Participant has died before such stock is sold, these holding period
requirements do not apply and no Disqualifying Disposition can occur
thereafter.

9.       ADJUSTMENT PROVISIONS.

         The aggregate number of shares of Common Stock with respect to which
Options may be granted, the aggregate number of shares of Common Stock subject
to each outstanding Option and the Option Price per share of each Option shall
all be appropriately adjusted if any of the following occur after the Plan's
adoption by the Board: any increase or decrease in the number of shares of
issued Common Stock resulting from a subdivision or consolidation of shares,
whether through reorganization, recapitalization, stock split, stock
distribution or combination of shares, or the payment of a share dividend or
other increase or decrease in the number of such shares outstanding effected
without receipt of consideration by the Company. Adjustments shall be made
according to the sole discretion of the Board, and its decision shall be binding
and conclusive.

10.      DISSOLUTION, MERGER AND CONSOLIDATION.

         Upon the dissolution or liquidation of the Company, or upon a merger or
consolidation of the Company in which the Company is not the surviving corpora-


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tion, the holder of each Option then outstanding under the Plan will thereafter
be entitled to receive at the next Exercise Date upon the exercise of such
Option for each share of Common Stock as to which such Option shall be
exercised, as nearly as reasonably may be determined, the cash, securities
and/or property which a holder of one share of the Common Stock was entitled to
receive upon and at the time of such transaction. The Board shall take such
steps in connection with such transactions as the Board shall deem necessary to
assure that the provisions of this Section 10 shall thereafter be applicable, as
nearly as reasonably may be determined, in relation to the said cash, securities
and/or property as to which such holder of such Option might thereafter be
entitled to receive.

11.      STOCKHOLDER APPROVAL.

         The Plan is subject to approval by the holders of a majority of the
outstanding shares of Common Stock (and the holders of any other class of stock
to the extent required by law, agreement or Section 423 of the Code) within 12
months before or after the date of adoption of the Plan by the Board. The Plan
shall be null and void and of no effect if the foregoing condition is not
fulfilled.

12.      MISCELLANEOUS.

         (a) LEGAL AND OTHER REQUIREMENTS. The obligations of the Company to
sell and deliver Common Stock under the Plan shall be subject to all applicable
laws, regulations, rules and approvals, including, but not by way of limitation,
the effectiveness of a registration statement under the Securities Act of 1933,
as amended, if deemed necessary or appropriate by the Company. Certificates for
shares of Common Stock issued hereunder may be legended to such effect as the
Board shall deem appropriate.

         (b) TERMINATION AND AMENDMENT OF PLAN. Except as provided in the
following sentence, the Plan may be terminated or amended by the stockholders of
the Company, by the Board, or by the Committee, including amendment of the Plan
from time to time to designate corporations whose employees may be offered
options under the Plan from among a group consisting of the Company and any
corporation which is or becomes its Affiliate. Amendments effecting: (1) any
increase in the aggregate number of shares of Common Stock which may be issued
under the Plan (other than an increase merely reflecting a change in
capitalization such as a stock dividend or stock split) or (2) changing the
designation of corporations whose employees may be offered options under the
Plan, except designations described in the preceding sentence, must be approved
by the stockholders of the Company within twelve (12) months after such
amendment is adopted by the Board or by the Committee or such amendment is void
ab initio. No amendment to the Plan shall affect any Options theretofore granted
or any Common Stock theretofore acquired by a


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Participant, unless such amendment shall expressly so provide and unless any
Participant to whom an Option has been granted who would be adversely affected
by such amendment consents in writing thereto. Unless otherwise determined by
the Board, no Options will be granted under the Plan after December 31, 2001.
The Plan shall expire on June 30, 2002, unless extended or earlier terminated in
accordance with the terms hereof.

         (c) WITHHOLDING TAXES. Upon a Disqualifying Disposition, within the
meaning of Section 8(d), of any shares of Common Stock received pursuant to the
exercise of any Option under the Plan, the Company shall have the right to
require the Participant to remit to the Company an amount sufficient to satisfy
all federal, state and local requirements as to income tax withholding and
employee contributions to employment taxes or, alternatively, in the Board's
sole discretion, the Company may withhold all such amounts from other
compensation due to the Participant by the Company.

         (d) RIGHT TO TERMINATE EMPLOYMENT. Nothing in the Plan or any agreement
entered into pursuant to the Plan shall confer upon any Eligible Employee or
other optionee the right to continue in the employment of the Company or any
Affiliated Company or affect any right which the Company or any Affiliated
Company may have to terminate the employment of such Eligible Employee or other
optionee.

         (e) RIGHTS AS A STOCKHOLDER. A Participant shall not have any right as
a stockholder of the Company with respect to shares of Common Stock issuable
pursuant to the exercise of an Option hereunder, unless and until a certificate
or certificates for such shares of Common Stock are issued to him or her or the
Company reflects the Participant's ownership in its stock ledger or other
appropriate record of Common Stock ownership.

         (f) LEAVES OF ABSENCE. The Board shall be entitled to make such rules,
regulations and determinations as it deems appropriate under the Plan in respect
of any leave of absence taken by any Eligible Employee, provided such rules are
consistent with Section 423 of the Code.

         (g) NOTICES. Every direction, revocation or notice authorized or
required by the Plan shall be deemed delivered to the Company (1) on the date it
is personally delivered to the Treasurer of the Company (or such other person as
may be designated by the Company from time to time with notice given to each
Participant) at its principal executive offices or (2) three business days after
it is sent by registered or certified mail, postage prepaid, addressed to the
Treasurer of the Company (or such other person as may be designated by the
Company from time to time with notice given to each Participant) at such offices
or (3) on the date on which delivery was guaranteed by a third party business
(such as Federal Express and including the


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postage service); and shall be deemed delivered to a Participant (A) on the date
it is personally delivered to him or her or (B) three business days after it is
sent by registered or certified mail, postage prepaid, addressed to him or her
at the last address shown for him or her on the records of the Company or of any
Affiliate or (C) on the date on which delivery was guaranteed by a third party
business (such as Federal Express and including the postal service), provided
that the documents were sent to him or her at the last address shown for him or
her on the records of the Company or of any Affiliate.

         (h) All Eligible Employees shall have the same rights and privileges
under the Plan, except that the amount of Common Stock which may be purchased
under Options granted under the Plan shall bear a uniform relationship to the
Compensation of Eligible Employees. All rules and determinations of the Board in
the administration of the Plan shall be uniformly and consistently applied to
all persons in similar circumstances.

         (i) APPLICABLE LAW. All questions pertaining to the validity,
construction and administration of the Plan and Options granted hereunder shall
be determined in conformity with the laws of the Commonwealth of Massachusetts,
to the extent not inconsistent with Section 423 of the Code and the regulations
thereunder.


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