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                                                                   EXHIBIT 10.55

                              AGREEMENT OF SUBLEASE

      This AGREEMENT OF SUBLEASE (this "Sublease") is made this 31st day of
December, 1999, by and between ARIAD Corporation ("Sublandlord"), and Aventis
Pharmaceuticals Inc. (formerly known as Hoechst Marion Roussel Inc.)
("Subtenant").

                                   BACKGROUND

      A. By Lease dated January 8, 1992 ("Original Lease"), ARIAD
Pharmaceuticals, Inc. leased from Forest City Cambridge, Inc. ("Prime Landlord")
certain space in the building known as The Jackson Building, having a street
address of 26 Landsdowne Street, Cambridge, Massachusetts ("Building"). The
Prime Lease Premises (defined below) are more particularly described in the
Prime Lease (defined herein), a copy of which is annexed hereto as Exhibit A.

      B. ARIAD Pharmaceuticals, Inc. assigned its interest in the Original Lease
to Sublandlord, which assignment was executed on October 19, 1992, and recorded
with the Middlesex County Southern District Registry of Deeds in Book 22527,
Page 581, and filed with the Middlesex County Southern Registry District of the
Land Court as Document No. 888025 noted on Certificate of Title No. 157415.

      C. The Original Lease as amended by the First and the Second Amendments to
Lease, each dated May 12, 1994, the Third Amendment to Lease, dated June 1,
1994, a letter agreement, dated December 16, 1996, a letter agreement dated July
31, 1998 and the Sixth Amendment to Lease, dated December 31, 1999 as the same
may from time to time be further amended and supplemented, are hereinafter
referred to collectively as the "Prime Lease." All of the space in the Building
that is now or hereafter leased by Sublandlord pursuant to the Prime Lease is
hereinafter referred to as the "Prime Lease Premises." The Prime Lease Premises
now contain 100,361 rentable square feet.

      D. Subject to and in accordance with the terms and conditions hereinafter
set forth, Sublandlord desires to sublease to Subtenant, and Subtenant desires
to rent from Sublandlord, that portion of the Prime Lease Premises which
comprises: (i) the entire space on the third floor in the Building containing
approximately 20,249 rentable square feet; (ii) the office and bioinformatics
space known as Suite 125 containing approximately 3,200 rentable square feet on
the first floor in the Building; (iii) the additional first floor office space
known as Suite 100, containing approximately 4,311 rentable square feet; and
(iv) the laboratory space on the fourth floor known as Suite 470, containing
approximately 6,605 square feet of rentable space. The foregoing shall
collectively be referred to as the "Subleased Premises." The Subleased Premises
is substantially shown on Exhibit B attached hereto.

      Capitalized terms used in this Sublease and not otherwise defined in this
Sublease shall have
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the meanings established in the Prime Lease.

      NOW, THEREFORE, in consideration of the covenants herein contained, the
parties hereto, intending to be legally bound hereby, do covenant and agree as
follows:

      1. Sublandlord's Representations. Sublandlord represents to Subtenant
that: (a) Exhibit A constitutes a true, correct and complete copy of the Prime
Lease as of the date hereof, and comprises the entire understanding and
agreement of Prime Landlord and Sublandlord with respect to the Prime Lease
Premises, (b) the Prime Lease is in full force and effect in accordance with its
terms, (c) to Sublandlord's knowledge neither Prime Landlord nor Sublandlord is
in default under the Prime Lease, and there exists no state of facts and no
event has occurred which, with the passage of time or the giving of notice, or
both, would constitute a default by either Prime Landlord or Sublandlord under
the Prime Lease and (d) Sublandlord is a wholly-owned subsidiary of ARIAD
Pharmaceuticals, Inc. During the Term of this Sublease, Sublandlord shall pay to
Prime Landlord when due all rent and all other charges reserved and covenanted
to be paid by the "Tenant" under the Prime Lease. Sublandlord agrees that it
will not agree to a termination of the Prime Lease unless in connection
therewith the Prime Landlord accepts this Sublease as a direct lease between
Prime Landlord and Subtenant. Additionally, Sublandlord agrees that it shall
not, prior to the expiration of this Sublease, remove any Optional Removable
Alterations, Required Removable Alterations or any other property owned by
Sublandlord and currently affixed to the Subleased Premises and used in
connection with the operations of the Subleased Premises.

      2. Subtenant's Representations. Subtenant shall observe and perform when
due all covenants, agreements and obligations of the "Tenant" under the Prime
Lease as the same shall apply to the Subleased Premises, except for "Tenant's"
obligation to pay rent. Subtenant's failure to perform "Tenant's" obligations
under the Prime Lease with respect to the Subleased Premises shall be a breach
of this Sublease and Sublandlord shall have all the rights against Subtenant as
would be available to Prime Landlord under the Prime Lease if such breach were
by "Tenant" thereunder. In the event of a default by Sublandlord under the Prime
Lease which results in the termination thereof, Subtenant shall, at the option
of Prime Landlord attorn to and recognize Prime Landlord as landlord hereunder
and shall, promptly upon the Prime Landlord's request, execute and deliver all
instruments necessary or appropriate to confirm such attornment and recognition.

      3. Incorporation of Prime Lease; Conflicting Terms. This Sublease is made
subject to and subordinate to all of the terms and conditions of the Prime Lease
and is conditioned upon the written approval of Prime Landlord. Insofar as the
Prime Lease relates to the Subleased Premises, each and every provision of the
Prime Lease shall be deemed incorporated herein and made a part of this
Sublease. The rights of Prime Landlord under the Prime Lease may be enforced by,
and are for the benefit of, both the Sublandlord herein and Prime Landlord.
Subtenant shall neither do nor permit anything to be done which would cause the
Prime Lease to be terminated or forfeited by reason of any right of termination
or forfeiture reserved or vested in "Prime Landlord" under the Prime Lease. Any
other provision of the Prime Lease or this Sublease to the contrary
notwithstanding, Subtenant shall not be responsible for (i) the obligation to
pay the Annual Fixed Rent, the real estate taxes and operating expenses
described in Paragraph 3 of the Prime Lease or any other charges reserved and
covenanted to be paid by the "Tenant" as "rent" under the Prime Lease,


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but shall be responsible to pay (a) Basic Rent (as herein defined) pursuant to
Section 7 herein and (b) its pro-rata share of all such charges to Sublandlord
as provided in Section 8 herein, (ii) any obligations of "Tenant" wherever
expressed in the Prime Lease to the extent that they relate to the removal of
improvements, alterations and additions to the Subleased Premises constructed
and installed by Prime Landlord or Sublandlord at or prior to the Commencement
Date of this Sublease, (iii) any obligations of "Tenant" wherever expressed in
the Prime Lease to the extent that they relate to the repair, replacement or
maintenance of a condition of the Subleased Premises existing at or prior to the
Commencement Date of this Sublease, (iv) any obligations of "Tenant" wherever
expressed in the Prime Lease relating to the indemnification of Prime Landlord
with respect to any loss, damage, liability, obligation, cost or expense arising
as a result of an act or omission that occurred prior to the Commencement Date
of this Sublease or arising as a result of a negligent act or omission of
Sublandlord, its agents, employees, contractors or invitees, (v) any obligations
of "Tenant" wherever expressed in the Prime Lease relating to the condition of
the Subleased Premises at the expiration of the term of this Sublease to the
extent that the required repair, maintenance or removal relates to a condition
existing on the Commencement Date of this Sublease and (vi) any obligations of
"Tenant" under the Prime Lease relating to any portion of the Prime Lease
Premises other than the Subleased Premises or arising prior to the Commencement
Date of this Sublease or arising after the date of expiration of the Term of
this Sublease (all of which obligations expressed in clauses (i) through (vi)
above shall be and remain the responsibility of Sublandlord). In the event that
any term or provision of the Prime Lease is inconsistent or conflicts with any
term or provision of this Sublease, the terms and provisions of the Prime Lease
shall control, except to the extent expressly provided herein.

      4. Sublease of Premises.

            4.01 For the Term (defined below) and upon the terms, covenants and
conditions herein set forth, Sublandlord hereby subleases to Subtenant, and
Subtenant hereby rents from Sublandlord, the Subleased Premises. During the Term
of this Sublease, but under and subject to the terms, covenants and conditions
of the Prime Lease, Subtenant shall have the right to use, together with
Sublandlord and the other tenants of the Building, the common public areas and
facilities of the Building, including, without limitation, the elevators
providing access to the Subleased Premises and the parking facilities, and to
receive and enjoy the benefit of the services and utilities required to be
provided to Sublandlord under the Prime Lease, but only to the extent that the
same pertain to the Subleased Premises.

            4.02 Without limitation of any of the terms of Section 4.01,
Subtenant shall have the right to the pro rata number of parking passes
allocable to the Subleased Premises (calculated on the basis of the measurement
method then used by Prime Landlord and Sublandlord under the Prime Lease for
such purposes).

      5. Sublease Term.

            5.01 Term. The term of this Sublease (including any renewals or
extensions thereof, "Term") shall commence on the date hereof (the "Commencement
Date") and, unless extended or sooner terminated as herein provided, end on July
31, 2002, the currently scheduled


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expiration date of the Prime Lease.

            5.02 Extension of Term. In the event Sublandlord extends the term of
the Prime Lease as therein provided, Sublandlord shall so notify Subtenant
promptly, and the Term of this Sublease, at the option of Subtenant, shall be
extended up to July 31, 2007 upon the same terms and conditions as herein
expressed and at the Basic Rent, which shall be the higher of: (i) a twenty-five
percent (25%) discount to the then current Fair Market Rental Value (as
hereinafter defined) of the Subleased Premises in its then condition ; or (ii)
the rate of the Annual Fixed Rent paid by Sublandlord to the Prime Landlord
under the Prime Lease, calculated to reflect only the premises then constituting
the Subleased Premises. Within thirty (30) days after Sublandlord notifies
Subtenant of the extension of the Term, Sublandlord shall also notify Subtenant
in writing of Sublandlord's reasonable determination of the Basic Rent for the
Subleased Premises during such extended Term, which amount shall be based on the
market rate. Such amount shall be the "Fair Market Rental Value" unless
Subtenant objects to Sublandlord's determination within fifteen (15) days from
Subtenant's receipt of Sublandlord's notice that Subtenant does not agree with
Sublandlord's determination, in which case the phrase "Fair Market Rental Value"
shall mean the then prevailing market rate for base minimum rental, calculated
on a per square foot basis for leases covering buildings comparable to the
Building (as adjusted for any variances between such buildings and the Building)
located in the Cambridge, Massachusetts metropolitan area (hereinafter referred
to as the "Market Area") as determined by the following appraisal procedure:

         In the event that Subtenant notifies Sublandlord that Subtenant
         disagrees with Sublandlord's determination of the Fair Market Rental
         Value for the extension Term, then Subtenant shall specify, in such
         notice to Sublandlord, Subtenant's selection of a real estate appraiser
         who shall act on Subtenant's behalf in determining the Fair Market
         Rental Value. Within twenty (20) days after Sublandlord's receipt of
         Subtenant's selection of a real estate appraiser, Sublandlord, by
         written notice to Subtenant, shall designate a real estate appraiser,
         who shall act on Sublandlord's behalf in the determination of the Fair
         Market Rental Value. Within twenty (20) days of the selection of
         Sublandlord's appraiser, the two (2) appraisers shall render a joint
         written determination of the Fair Market Rental Value, which
         determination shall take into consideration any differences between the
         Building and those buildings comparable to the Building located in the
         Market Area, including without limitation age, location, setting and
         type of building. If the two (2) appraisers are unable to agree upon a
         joint written determination within said twenty (20) day period, the two
         appraisers shall select a third appraiser within such twenty (20)
         period. Within twenty (20) days after the appointment of the third
         appraiser, the third appraiser shall render a written determination of
         the Fair Market Rental Value. The average of the three determinations
         shall be the final and conclusive Fair Market Rental Value. All
         appraisers selected in accordance with this Section shall have at least
         ten (10) years prior experience in the commercial leasing market of the
         Market Area and shall be members of the American Institute of Real
         Estate Appraisers or similar professional organization. If either
         Sublandlord or Subtenant fails or refuses to select an appraiser, the
         other appraiser shall alone determine the Fair Market Rental Value.
         Sublandlord and Subtenant agree that they shall be bound by the
         determination of


                                       4
<PAGE>
         Fair Market Rental Value pursuant to this Section. Sublandlord shall
         bear the fee and expenses of its appraiser; Subtenant shall bear the
         fee and expense of its appraiser; and Sublandlord and Subtenant shall
         share equally the fee and expenses of the third appraiser, if any.

      6. Access to Subleased Premises. Subtenant and its agents, employees and
business invitees shall have the right, in common with Sublandlord, to use the
elevator lobbies and common hallways of the Building 24 hours per day, 7 days
per week in accordance with the Prime Landlord's rules and regulations, for the
sole purpose of obtaining ingress to and egress from the Subleased Premises.
Subtenant and its agents, employees and business invitees also shall have the
right, in common with Sublandlord, to use the common area lavatory facilities of
the Building. Sublandlord and Subtenant shall cooperate with each other to
facilitate Subtenant's shipping and receiving of Subtenant's materials and
supplies to and from the Subleased Premises; without limiting the foregoing,
Subtenant and its agents, employees and business invitees shall have the right,
in common with Sublandlord, to use the loading dock.

      7. Rent. Subtenant shall pay Sublandlord rent ("Basic Rent") at an amount
equal to (i) for the entire space on the third floor in the Building containing
approximately 20,249 rentable square feet, at a rate of $12.00 per square foot,
$242,988.00; (ii) for the office and bioinformatics space known as Suite 125
containing approximately 3,200 rentable square feet on the first floor in the
Building, at a rate of $20.00 per square foot, $64,000.00; (iii) for the
additional first floor office space known as Suite 100, containing approximately
4,311 rentable square feet, at a rate of $20.00 per square foot, $86,220.00; and
(iv) for the laboratory space on the fourth floor known as Suite 470, containing
approximately 6,605 square feet of rentable space, at a rate of $39.00 per
square foot, $257,595.00; the sum of such amounts being $650,803.00 on an annual
basis, payable in equal monthly installments of $54,233.58, in advance, on the
first day of each month during said term, at the office of Sublandlord or such
other place as Sublandlord may designate, without any set off, counterclaim or
deduction whatsoever. The foregoing notwithstanding, during the extended term if
any of this sublease, Subtenant shall pay Sublandlord Basic Rent as calculated
in accordance with Section 5.02 above. If the Commencement Date should occur on
a day other than the first day of a calendar month, or if this Sublease shall
expire or terminate on a day other than the last day of a calendar month, then
the rent for such fractional month shall be prorated on a daily basis based upon
a thirty (30) day calendar month.

      8. Additional Rent.

            8.01 From and after the Commencement Date, and throughout the Term
of this Sublease, Subtenant shall pay as additional rent ("Additional Rent",
Basic Rent and Additional Rent, and each installment and/or increment thereof,
are sometimes herein collectively called "rent") Subtenant's allocable share of
all additional (i.e., in addition to the Basic Rent) sums, costs, expenses and
other payments that Sublandlord is obligated to pay Prime Landlord under the
Prime Lease to the extent attributable to the Subleased Premises, including,
without limitation, the following: (i) Subtenant's Proportionate Share (defined
below) of Tenant's Tax Expense Allocable to the Prime Lease Premises (as
provided in Section 3.2 of the Prime Lease); (ii) Tenant's parking charges as


                                       5
<PAGE>
provided in Section 2.4 of the Prime Lease with respect to those parking passes
to which Subtenant is entitled hereunder; (iii) Subtenant's Proportionate Share
of Tenant's Operating Expenses Allocable to the Prime Lease Premises in
accordance with Section 3.3 of the Prime Lease; and (iv) amounts payable for
special services requested by or exclusively benefitting Subtenant pursuant to
Section 3.5 of the Prime Lease. For the purposes of this Sublease, Subtenant's
Proportionate Share shall mean a fraction, the numerator of which is the number
of rentable square feet within the Subleased Premises and the denominator of
which is the Sublandlord's Rentable Floor Area.

            8.02 In addition to the costs described in 8.01, Subtenant shall pay
to Sublandlord as Additional Rent (i) Subtenant's Proportionate Share of
Sublandlord's cost of providing lighting, heating, air conditioning and other
utilities to the common lobbies, hallways, stairways, bathrooms and other shared
areas within the Prime Lease Premises; (ii) Subtenant's allocable share of the
salaries, benefits and other compensation paid by Sublandlord to the Building
Manager and the Facilities Engineer for the Prime Lease Premises determined in
accordance with Schedule 8.02 attached hereto (it being understood that the
salaries, benefits and other compensation paid to such persons shall not exceed
the prevailing wages, benefits and compensation packages paid by Sublandlord to
other employees with comparable experience and qualifications); and (iii)
Subtenant's allocable share of Sublandlord's cost of providing special
utilities, support and services to or for the benefit of the Subleased Premises
as generally described on Schedule 8.02 attached hereto, it being understood
that Section 8.02 is merely a "good faith" estimate of the costs to be incurred
by Sublandlord in order to provide such special utilities, support and services
to the Subleased Premises, and not a limitation on the categories or amounts of
expenses for which Subtenant is responsible. If, during the Term of this
Sublease, Sublandlord incurs costs of a capital nature in connection with
Sublandlord's provision of any of the utilities, support or services described
in this Section 8.02, Subtenant's Proportionate Share of such capital item
during any calendar year or other twelve (12) month accounting period selected
by Sublandlord shall be limited to the annual amortization of the cost of the
capital item (calculated, with interest, over the useful life of the item as
reasonably determined by Sublandlord). Subtenant also shall pay directly to the
provider of the service all charges for separately metered utilities consumed by
Subtenant within the Subleased Premises.

            8.03 Sublandlord understands that confidential information will be
stored in the Subleased Premises and, therefore, Subtenant will not permit any
unauthorized persons or authorized persons unattended into the Subleased
Premises. Notwithstanding the foregoing, the Building Manager and the Facilities
Manager shall have limited access to the Subleased Premises, provided that an
employee of Subtenant shall accompany the Building Manager and the Facilities
Manager into the Subleased Premises at all times, without exception, subject to
such confidentiality requirements imposed by Subtenant from time to time.
Notwithstanding the foregoing, Sublandlord shall in the event of an emergency
use its best efforts to notify Subtenant prior to its entry into the Subleased
Premises and in any event will notify Subtenant of such entry as soon as
reasonably possible.

            8.04 Sublandlord shall maintain true and complete books of account
containing an accurate record of the data necessary for the proper determination
and computation of all amounts to be paid by Subtenant to Sublandlord under the
terms of this Section to the extent provided by the


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Prime Landlord to Sublandlord; provided, however, that Sublandlord shall not be
required hereby to maintain any duplicate books of account or records.
Sublandlord shall retain and maintain such records in accordance with
Sublandlord's records retention policy for its other books and records; provided
however, such retained records shall not be destroyed without the consent of
Subtenant (such consent not to be unreasonably withheld). Subtenant shall have
the right, using the firm of independent certified public accountants employed
by Sublandlord to conduct Sublandlord's regular annual audit, or another
national firm of independent certified Sublandlord accountants acceptable to
Sublandlord (whose approval of such accountants will not be unreasonably
withheld), to audit such books for the purpose of verifying such amounts. Such
examination shall be made upon reasonable advance notice to Sublandlord during
normal business hours at Sublandlord's principal office. In the event that the
result of any such audit is less than the amount invoiced by Sublandlord and
such difference exceeds five percent (5%) of the invoiced amount, Sublandlord
shall promptly pay to Subtenant the full amount of such difference. In the event
that the result of any such audit is greater than the amount invoiced by
Sublandlord and such difference exceeds five percent (5%) of the invoiced
amount, Subtenant shall promptly pay to Sublandlord the full amount of such
difference. The cost of any such audit shall be borne by, in the event that any
such difference is more than five percent (5%) of the invoiced amount, the
paying party, and, in the event that any such difference is less than five
percent (5%) of the invoiced amount, the requesting party.

            8.05 Security Deposit. Subtenant acknowledges that, as required by
Section 12.11 of the Prime Lease, Sublandlord has provided Prime Landlord with a
bank letter of credit in the amount of $327,646 ("Letter of Credit") to secure
timely performance by Sublandlord of its obligations as "Tenant" under the Prime
Lease. In lieu of providing a cash security deposit to Sublandlord hereunder,
Subtenant shall pay to Sublandlord as Additional Rent Subtenant's Proportionate
Share of Sublandlord's cost of providing and maintaining the Letter of Credit,
which cost shall be calculated as the sum of (i) Subtenant's Proportionate Share
of any fees or costs paid by Sublandlord during the Term of this Sublease for
the continued issuance of the Letter of Credit (not to exceed 1.5% per annum of
the stated amount of the Letter of Credit) and (ii) an amount computed at an
interest rate equal to the "Prime Lending Rate" as determined on December 1st of
each year by the Wall Street Journal per annum of Subtenant's Proportionate
Share of the amount of cash or cash equivalent security (not to exceed 120% of
the stated amount of the Letter of Credit), if any, pledged by Sublandlord as
collateral security for the Letter of Credit. The amount of Additional Rent
payable by Subtenant pursuant to this Section 8.05 shall adjust from time to
time if, as and when the stated amount of the Letter of Credit is adjusted. If
during the Term of this Sublease Sublandlord elects to replace the Letter of
Credit with cash or cash equivalent security deposited with Prime Landlord, the
Additional Rent payable by Subtenant pursuant to this Section 8.05 shall equal
an amount computed using an interest rate calculated as the "Prime Lending Rate"
as determined on December 1st of each year by the Wall Street Journal per annum
of Subtenant's Proportionate Share of the cash or cash equivalent security
deposited from time to time with Prime Landlord.

      9. Use. Subtenant shall use and occupy the Subleased Premises for general
offices, technical offices for research and development, laboratories and
research facilities, manufacturing of drugs and the fabrication, assembling,
finishing work and packaging of such drugs, subject, however to Section 6.2 of
the Prime Lease.


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      10. Insurance.

            10.01 Notwithstanding anything herein to the contrary, to the extent
that either party is required by the provisions of this Sublease or the Prime
Lease to carry insurance, each party hereto hereby releases the other party, its
directors, officers, agents, employees and servants to the extent of the
releasing party's actual recovery under its insurance policies, from any and all
liability or responsibility to it or anyone claiming by, through or under it or
them by way of subrogation or otherwise, for any loss or damage which may be
inflicted upon the property of such party, notwithstanding that such loss or
damage shall have arisen out of the negligent or intentionally tortious act or
omission of the other party, its agents or employees.

            10.02 Each insurance policy that either party is required or
authorized to carry hereunder shall contain a clause that the release provided
herein shall not affect the policy. Each insurance policy that either party is
required to carry hereunder shall contain a waiver of any right of subrogation
against the other party. Sublandlord and Subtenant hereby waive any right of
subrogation against each other on behalf of any and all insurers providing
insurance required by the terms hereof.

            10.03 Subtenant, at its sole expense, shall maintain for the benefit
of Sublandlord and Prime Landlord, such policies of insurance (and in such form)
as are required by the Prime Lease with respect to the Subleased Premises, which
policies shall be reasonably satisfactory to Sublandlord and Prime Landlord as
to coverage and insurer. Each such policy shall name Sublandlord and Prime
Landlord as additional insured parties.

      11. Hold Harmless. Neither Sublandlord nor Subtenant shall do or cause to
be done, or suffer or permit any act or thing to be done, which may cause the
Prime Lease or the rights of Sublandlord or Subtenant to be canceled,
terminated, forfeited or prejudiced or which may make the other party liable for
any damages, claims, fines, penalties, costs or expenses thereunder. Each of the
Sublandlord and Subtenant shall indemnify and save harmless the other from all
suits, actions, judgments, damages, claims, liabilities, awards, losses, fines
penalties, costs, charges and expenses, including attorneys fees, that either
may sustain by reason of the other's failure to perform the terms of this
Sublease or the Prime Lease or by reason of the breach by the other of any of
the terms, covenants or conditions of this Sublease or the Prime Lease except
those arising out of the negligent acts or omissions of the party being
indemnified.

      12. Condition of Subleased Premises. Subtenant hereby leases the Subleased
Premises, and accepts them "as is - where is" in their present condition, as a
result of whatever inspecting Subtenant deemed necessary, and not as a result of
or in reliance upon any representation or warranty of any nature whatsoever by
Sublandlord, or any employee or agent of Sublandlord. Sublandlord shall use
commercially reasonable efforts to provide Subtenant access to the Subleased
Premises prior to the Commencement Date for Subtenant to install furniture,
fixtures, office and telecommunications equipment and other items necessary for
Subtenant to conduct its business provided that Subtenant provides Sublandlord
and any contractors and/or subcontractors provide Sublandlord a copy of its
certificate of insurance evidencing the insurance policy required hereunder to
be obtained by Subtenant, naming Sublandlord and Prime Landlord as additional
insureds prior to


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any such access.

      13. Services.

            13.01 Where in the Prime Lease there are duties and obligations owed
by Prime Landlord to Sublandlord that are necessary for the proper use and
enjoyment of the Subleased Premises by Subtenant under this Sublease,
Sublandlord shall use commercially reasonable efforts to obtain the performance
of such duties and obligations by Prime Landlord in favor of Subtenant, but
Sublandlord shall not be liable to Subtenant for the failure of Prime Landlord
to perform said duties and obligations or for the result of such failure. The
only services or rights to which Subtenant is entitled hereunder are those to
which Sublandlord is entitled under the Prime Lease. Notwithstanding the
foregoing, if Prime Landlord shall default in any of its obligations to
Sublandlord with respect to the Subleased Premises, Subtenant shall be entitled
to participate with Sublandlord in the enforcement of Sublandlord's rights
against Prime Landlord. If, after written request from Subtenant, Sublandlord
shall fail or refuse to take appropriate action for the enforcement of
Sublandlord's rights against the Prime Landlord with respect to the Subleased
Premises within a reasonable period of time considering the nature of Prime
Landlord's default, Subtenant shall have the right to take such action in its
own name, and for that purpose and only to such extent, all of the rights of
Sublandlord under the Prime Lease hereby are conferred upon and assigned to
Subtenant and Subtenant hereby is subrogated to such rights to the extent that
the same shall apply to the Subleased Premises. Sublandlord hereby grants
Subtenant the right to deal directly with Prime Landlord with respect to any
rights of Sublandlord as Tenant under the Prime Lease which are exercisable with
respect to the Subleased Premises, the conduct or manner of conduct of
Subtenant's or Prime Landlord's activities therein or work to be performed or
services to be rendered therein or thereto by Prime Landlord; it being the
intent of the parties hereto that Subtenant may exercise such rights as are
reasonably necessary or desirable to permit Subtenant to use and occupy the
Subleased Premises on a regular basis as contemplated in this Sublease, and not
otherwise.

            13.02 Sublandlord covenants and agrees to use commercially
reasonable efforts to: (i) furnish to Subtenant the special utilities and other
services described in Schedule 8.02; and (ii) provide the employees identified
in Schedule 8.02. Sublandlord further covenants and agrees to make available
such employees to respond promptly to any problems, complaints or other service
requests related to the Building for which Subtenant notified Sublandlord.
Notwithstanding the foregoing, Subtenant shall have the right to deal directly
with such employees with respect to any such notifications.

      14. Subletting and Assignment.

            14.01 Subtenant shall not assign or sublet the Subleased Premises
without first providing Sublandlord one hundred eighty (180) days written notice
of such proposed assignment or sublease whereupon Sublandlord shall have the
option within ninety (90) days of receipt of such notice to either consent to
such assignment or sublease or terminate this lease and repossess the space
proposed to be assigned or sublet. In the event Sublandlord approves such
assignment or sublease, Subtenant shall pay to Sublandlord one hundred percent
(100%) of all the rent and any and all additional compensation received from
such sublessee above the Basic Rent paid owed by


                                       9
<PAGE>
Subtenant to Sublandlord under the terms of this Sublease. Notwithstanding the
foregoing to the contrary, Subtenant shall not be released of any liability
under this Sublease.

            14.02 Notwithstanding the provisions of Section 14.01, either party
may assign this Sublease to any Affiliate (as defined below) or in connection
with the sale of all or substantially all of such party's assets. For the
purposes of this Sublease, "Affiliate" shall mean any corporation, firm,
partnership or other entity which directly or indirectly controls or is
controlled by or is under common control with a party to this Sublease.
"Control" means ownership, directly or through one or more Affiliates, of more
than fifty percent (50%) of the shares of stock entitled to vote for the
election of directors, in the case of a corporation, or more than fifty percent
(50%) of the equity interests in the case of any limited liability company or
other type of legal entity, status as a general partner in any partnership, or
any other arrangement whereby a party controls or has the right to control the
board of directors or equivalent governing body of a corporation or other
entity.

      15. Approvals and Consents. If Sublandlord's consent or approval of a
request from Subtenant requires Sublandlord to obtain the consent or approval of
Prime Landlord, then any consent or approval from Sublandlord is subject to
receiving consent or approval from Prime Landlord and Sublandlord shall forward
any such request in a timely manner.

      16. Binding Effect. The provisions of this Sublease shall be binding upon
and inure to the benefit of the parties hereto and their respective legal
representatives, successors and assigns. This Sublease constitutes the entire
agreement between the parties hereto and may not be modified except by an
instrument in writing signed by the parties hereto.

      17. Notices. Whenever it shall be necessary or desirable for either party
to this Sublease to serve any notice or demand on the other party, such notice
or demand shall be served by certified mail, return receipt requested, by
overnight courier (such as Federal Express), next day delivery, or telecopy, at
the addresses set forth below or at such other address as shall be designated by
the parties in accordance with this Section. Each party shall provide to the
other copies of all notices received by each from Prime Landlord.

      If to Sublandlord:

                  ARIAD Corporation
                  26 Landsdowne Street
                  Cambridge, MA  02139
                  Attn: Chief Executive Officer
                  Telecopy:  (617) 494-8144

      With copy to:

                  Mintz, Levin, Cohn, Ferris, Glovsky and Popeo. P.C.
                  One Financial Center
                  Boston, MA 02111
                  Attn: Joel Bloom, Esq.


                                       10
<PAGE>
                  Telecopy: (617)542-2241

      If to Subtenant:

                  Aventis Pharmaceuticals Inc.
                  Route 202-206
                  P.O Box 6800
                  Bridgewater, NJ  08807
                  Attn:  Vice President and General Counsel,
                         Global Drug Development Center
                  Telecopy:  (908) 231-4480

      With copy to:

                  Morgan, Lewis & Bockius LLP
                  1701 Market Street
                  Philadelphia, PA  19103-2921
                  Attn: Edward J. Matey Jr., Esquire
                  Telecopy:  (215) 963-5299

      18. Amendments. No amendments shall be made to this Sublease without the
prior written approval of Prime Landlord in accordance with the terms of the
Prime Lease.

      19. Counterparts. This Sublease may be executed in counterparts.

                  [Remainder of page intentionally left blank.]


                                       11
<PAGE>
         IN WITNESS WHEREOF, Sublandlord and Subtenant have executed this
Sublease as of the date first above written.

                                               SUBLANDLORD:

(Corporate Seal)                               ARIAD Corporation


Attest:   /s/ Harvey J. Berger                 By:    /s/ Jay R. LaMarche
          --------------------                        -------------------
          Name:    Harvey J. Berger                   Name:  Jay R. LaMarche
          Title:   President                          Title: Treasurer


                                               SUBTENANT:

(Corporate Seal)                               Aventis Pharmaceuticals Inc.


Attest:   /s/                                  By:    /s/ Frank L. Douglas
          --------------------                        --------------------
          Name:                                       Name:  Frank L. Douglas
          Title:                                      Title: Vice President


                                       12
<PAGE>
                                    EXHIBIT A

                          [Attach Copy of Prime Lease]
<PAGE>
                                    EXHIBIT B

                       [Description of Subleased Premises]
<PAGE>
                                  SCHEDULE 8.02