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                                                                  EXHIBIT 10.50


                                   SUBLEASE


      SUBLEASE made as of the 28th day of June, 1996 ("the Sublease") between
PERSEPTIVE BIOSYSTEMS, INC., a Delaware corporation, as sublessor ("Landlord"),
having an address at 500 Old Connecticut Path, Framingham, MA 01701 and
CHEMGENICS PHARMACEUTICALS INC., a Delaware corporation, as sublessee
("Tenant"), having an address at One Kendall Square, Building 300, Cambridge,
Massachusetts 02139.

      Pursuant to a Lease dated as of May 24, 1994 (the "Overlease") between 500
Old Connecticut Path Limited Partnership, a Delaware Limited Partnership (the
"Overlandlord") and Landlord, the Overlandlord leased to Landlord certain
premises (the "Premises") more fully described in the Overlease as Buildings A
and B (the "Buildings") known as and located at 500 Old Connecticut Path,
Framingham, Massachusetts (the "Property"). The Overlease is attached hereto as
Exhibit A.

      Landlord desires to sublease a certain part of the Premises located in
Building A to Tenant, and Tenant desires to sublease the same from Landlord, for
the term and upon the terms and conditions hereinafter set forth.

      NOW, THEREFORE, for One Dollar and other good and valuable consideration,
and in consideration of the mutual covenants set forth herein, the parties
hereby agree as follows:

ARTICLE 1.  DEFINITIONS:

      Section 1.1. "Commencement Date" shall mean the later of June 28, 1996 or
the Overlandlord Consent Date.

      Section 1.2. "Demised Premises" shall mean (a) during the Initial Term,
that portion of the Premises, which the parties hereto agree contains
approximately 4870 square feet of Rentable Floor Area (as defined in the
Overlease) on the third floor of Building A, shown cross-hatched on Exhibit B
attached hereto (the "Third Floor Premises") and (b) in substitution therefor
during the Extended Term, that portion of the Premises which the parties hereto
agree contains approximately 20,000 square feet of Rentable Floor Area on the
second floor of Building A, shown as "expansion", and consisting of two such
areas on Exhibit B and such additional offices in between or adjoining such
areas, comprising up to approximately 10,000 square feet, as the parties may
agree to include ("Second Floor Premises"), such Second Floor Premises to be
definitively determined as provided in Section 5.2 hereinbelow.

      Section 1.3. "Extended Term" shall mean the period from the Rent
Commencement Date--Third Floor through the Termination Date.
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      Section 1.4. "Initial Term" shall mean the period from the Commencement
Date to the Rent Commencement Date--Third Floor.

      Section 1.5. "Landlord" and all pronouns referring thereto shall mean the
Landlord named herein and the successors, legal representatives and assigns of
such Landlord collectively.

      Section 1.6. "Rent Commencement Date--Third Floor" shall mean the date of
closing of the IPO as hereafter defined. "Rent Commencement Date--Second
Floor" shall mean three months after the date of the closing on the initial
Public Offering ("IPO") of the stock of the Tenant, as the IPO is defined in
Section 8.06 of the Master Agreement.

      Section 1.7. "Sublease" shall mean this instrument and any provisions of
the Overlease incorporated herein by reference.

      Section 1.8. "Tenant" and all pronouns referring thereto shall mean the
Tenant named herein and the successors, legal representatives and assigns of
such Tenant collectively.

      Section 1.9. "Tenant's pro rata share of common areas" shall mean during
the Initial Term 1408 square feet and during the Extended Term the Rentable
Square Feet of the Demised Premises divided by 186,060 Rentable Square Feet
times 21,000 [the common areas Tenant has access to during the Extended Term]
square feet.

      Section 1.10. "Termination Date" shall mean the earlier of June 27, 2001
or the Early Termination Date as described in Section 3.2, unless sooner
terminated, as provided herein or such other date as to which Landlord and
Tenant may agree as set forth in Section 5.2.

      Section 1.11. "Permitted Use" shall be use in connection with Tenant's
drug discovery business as a laboratory, research and development facilities and
office uses and other lawful uses included within the definition of "Permitted
Uses" in Exhibit A of the Overlease which are necessary or incidental to
Tenant's drug discovery business in compliance with all laws, regulations,
permits and the like, and, except to the extent otherwise agreed to in writing
by Landlord, such use shall be substantially similar to Landlord's drug
discovery business previously conducted in the Buildings.

      Section 1.12. "Overlandlord Consent Date" shall mean the date when the
consent of the Overlandlord to this Sublease has been obtained, pursuant to
Section 17.3 hereof.

ARTICLE 2.  DEMISE:


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      Section 2.1. Landlord hereby subleases the Demised Premises to Tenant, and
Tenant hereby subleases the Demised Premises from Landlord, for the Permitted
Use upon the terms, provisions and conditions in this Sublease contained, and
except as otherwise expressly provided in this Sublease, subject to the terms,
provisions and conditions of the Overlease.

      During the Initial Term Tenant shall have, as appurtenant to the Demised
Premises, the non-exclusive right to use in common with Landlord and others
entitled thereto, subject to Landlord's reasonable rules relating thereto, the
areas marked with an "X" or an arrow on Exhibit B. During the Extended Term,
Tenant shall have such rights to all such areas except those on the third floor
and the stairwell and elevator to the third floor.

      Section 2.2. The Tenant covenants and agrees that it will not enter any
other portion of the Premises at the Buildings at any time for any purpose
without Landlord's express consent, that it will not in any way interfere with
Landlord's business operations or Landlord's use and occupancy of the Premises,
nor will it permit any such interference, and that it will comply with all of
Landlord's security and/or confidentiality measures and procedures, health and
safety procedures and any other reasonable rules and regulations of Landlord
regarding the use and occupancy of the Demised Premises, the Premises and the
Property Common Areas described in the Overlease. The foregoing shall not be
deemed to impose a duty upon Landlord with respect to such matters, it being
understood that Tenant shall remain solely responsible for its own security,
confidentiality, health and safety and that of its property, employees and
invitees. Tenant will install locks on the laboratories contained within the
Demised Premises and shall be solely responsible for its personal property and
security as to the Demised Premises and its contents, including personal and
other property, but not the balance of the Premises or the contents thereof.

ARTICLE 3.  TERM OF SUBLEASE:

      Section 3.1. The term of this Sublease (the "Term") shall begin on the
Commencement Date and shall expire at midnight on the Termination Date, unless
such Term shall sooner cease and expire as hereinafter provided. As of the date
of execution of this Sublease, Landlord agrees to allow Tenant access to the
Demised Premises prior to the Commencement Date to begin (in accordance with the
provisions of Section 5.1 of this Sublease) preparing the Demised Premises for
Tenant's occupancy. Tenant shall have no obligation hereunder to pay rent or
other charges at any time prior to the Commencement Date, except as otherwise
agreed in writing by Tenant.

      Section 3.2. Landlord shall be entitled to terminate this Sublease upon 30
days written notice in the event of the


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rescission pursuant to Section 8.07 of the Master Agreement between Landlord and
Tenant dated May 7, 1996. The effective date of termination, which shall be set
out in Landlord's notice, shall be referred to as the "Early Termination Date".

ARTICLE 4.  FIXED RENT AND ADDITIONAL RENT:

      Section 4.1. Tenant covenants and agrees to pay to Landlord, as Fixed Rent
for the Demised Premises as follows:

      A. From the Commencement Date until the Rent Commencement
      Date--Third Floor, the sum of $1.00,

      B. From the Rent Commencement Date--Third Floor through 5/23/99, the sum
      of $5.75 per Rentable Square Foot of Demised Premises plus $5.75 times
      Tenant's pro rata share of common areas per year, payable in equal monthly
      installments of 1/12 of said sum in advance on the first day of each and
      every calendar month during the Term, and pro rata for any fraction of a
      month,

      C. From 5/24/99 through the Termination Date, the sum of $7.00 per
      Rentable Square Foot of Demised Premises plus $7.00 times Tenant's pro
      rata share of common areas per year, payable in equal monthly installments
      of 1/12 of said sum in advance on the first day of each and every calendar
      month during the Term, and pro rata for any fraction of a month.

      D. Fixed Rent is intended to equal the total of (1) a pro rata share of
Landlord's Fixed Rent under the Overlease, i.e., (the Fixed Rent per Rentable
Square Foot ("RSF") x (the RSF of the Second Floor Premises (approx. 20,000 -
30,000 sq. ft.)) plus (2) Tenant's pro rata share of the Fixed Rent attributable
to the Tenant's use of the common areas, i.e., (20,000 - 30,000 RSF/186,060 RSF)
x [COMMON AREAS TO WHICH TENANT HAS ACCESS] x (Fixed Rent per RSF).

      For example: Assume that the second floor space is 20,000 RSF, the total
      common areas shared by Landlord and Tenant is 21,000 RSF, the Fixed Rent
      per RSF is $5.75, and the Buildings are 186,060 RSF. Thus, Tenant is
      subleasing 10.7% of the total Landlord's Rentable Square Feet. The Fixed
      Rent starting with the Rent Commencement Date--Second Floor would be a
      total of (a) $5.75 x 20,000 = $115,000 plus (b) 10.7% x $5.75 x 21,000 =
      $12,920 or $127,920.

Notwithstanding anything to the contrary herein contained, the Fixed Rent listed
in subsections B, C and D of the preceding sentence is to be exactly equal to
the Fixed Rent per square foot of Rentable Floor Area paid by Landlord under the
Overlease, as


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reduced by any abatements in the Overlease or otherwise, if applicable to the
Demised Premises.

      Section 4.2. Commencing on the Rent Commencement Date--Third Floor Tenant
shall also pay directly to Landlord, on the first day of each and every month
during the Term, or, at Landlord's option, within 10 business days of demand, as
Additional Rent, its pro rata share ("Tenant's Share") of all Real Estate Taxes
which Landlord is obligated to pay under Section 3.2 of the Overlease. "Tenant's
Share" shall be computed from time to time on the basis of a fraction whose
numerator is the number of square feet of Rentable Floor Area in the Demised
Premises plus Tenant's pro rata share of common areas and whose denominator is
the total number of square feet of Rentable Floor Area leased by Landlord under
the Overlease.

      Section 4.3. Commencing on the Rent Commencement Date--Third Floor,
Tenant shall also pay directly to Landlord, on the first day of each and every
month during the Term, or, at Landlord's option, within 10 business days of
demand, as Additional Rent, Tenant's Share of all Operating Expenses and other
charges which Landlord is obligated to pay under Sections 3.3 through 3.6 of the
Overlease.

      Section 4.4. Commencing on the Rent Commencement Date--Third Floor,
Tenant shall also pay directly to Landlord, on the first day of each and every
month during the Term, or, at Landlord's option, within ten (10) business days
of demand, and as Additional Rent, Tenant's Share of all other charges payable
now or in the future under the Overlease (as it may be amended, so long as such
amendment as it affects Tenant's obligations hereunder directly benefits the
Demised Premises or the common areas shared by Tenant) by Landlord, as tenant
under the Overlease, excluding any late fees or penalties and any amounts owing
as a result of a default by Landlord as tenant under the Overlease unless
resulting from a default by Tenant hereunder plus Tenant's Share of third party
costs paid by Landlord which in Landlord's reasonable determination, directly
benefit the Demised Premises or the common areas shared by Tenant.

      Section 4.5. Tenant shall have the right to use Tenant's Share of the
parking spaces leased by Landlord under the Overlease.

      Section 4.6. Tenant covenants and agrees that the Fixed Rent and all
Additional Rents, charges and adjustments hereunder shall be paid to Landlord in
legal tender of the United States of America, at Landlord's address set forth
above, Attention: Accounting Manager or at such other place or to such other
person's attention as Landlord may from time to time designate by notice in
writing.


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      Section 4.7. It is intended by the Landlord and Tenant that Tenant pay
Tenant's Share of the Fixed Rent and Additional Rent and other sums due the
Overlandlord pursuant to Sections 3.3 - 3.6 of the Overlease but that there be
no profit to Landlord in connection with any payments hereunder.

ARTICLE 5. ACCEPTANCE OF DEMISED PREMISES; TENANT'S IMPROVEMENTS:

      Section 5.1. Tenant agrees to accept and does accept possession of the
Demised Premises on the Commencement Date "as is" in the same condition as they
are on the date hereof, free of any other tenants. The Tenant has had the
opportunity to conduct its own investigations with respect to the Demised
Premises and the Buildings to otherwise satisfy itself that the Demised
Premises, the Buildings and the Property (as defined in the Overlease) are
suitable for the conduct of Tenant's business. The Tenant acknowledges that
except as set forth expressly in this Sublease, there have been and are no
representations or warranties made by or on behalf of the Landlord with respect
to the Demised Premises, the Building or the Property, or with respect to the
suitability of any of them for the conduct of the Tenant's business. Landlord
shall have no obligation to perform any work or construction with respect to the
Demised Premises as a condition to or subsequent to the commencement of this
Sublease, including any telephone and computer cabling, which shall be Tenant's
responsibility. Tenant shall not in any way make any alterations, additions or
changes to the Demised Premises without having first secured the written
permission of Landlord and, if required by the Overlease, by Overlandlord in
accordance with the Overlease. Any work shall be done in accordance with the
plans and specifications submitted to and approved by Landlord and if required
by the Overlease, Overlandlord and in all other respects in accordance with
Article 4 of the Overlease.

      Any alterations made by or for Tenant shall be done at Tenant's sole cost
and expense in a good and workmanlike manner using new materials of first-class
quality consistent with the style and finish of the Demised Premises. Tenant
shall secure all necessary permits in advance of commencement of any work and
shall keep the Demised Premises free of any mechanics' or other liens and shall
hold Landlord and Overlandlord harmless from any loss, cost or damage arising
out of any work done by or for Tenant or by its agents or contractors. Landlord
shall have the right to remove unpermitted alterations at Tenant's cost. All
contractors working for Tenant in the Demised Premises shall be properly
insured, with such insurance as is required under Article 4 of the Overlease and
shall provide certificates of insurance naming Landlord and Overlandlord as
additional named insureds prior to commencement of any work. Tenant, at the
expiration of the Term or earlier termination of this Sublease,


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shall deliver the Demised Premises to Landlord in the same condition as they
were on the Commencement Date, reasonable wear and tear and damage by fire or
other casualty only excepted and Tenant shall remove all personal goods and
effects of Tenant leaving the Demised Premises neat, clean and in first-class
rentable condition and shall remove any alterations if and as required under the
Overlease and as requested by Landlord prior to the time of their installation
and repairing damage arising therefrom.

      Section 5.2. On or before the day which is 1 month after the date of the
closing of the IPO, Tenant shall notify Landlord in writing whether it elects to
proceed with occupancy and buildout of the Second Floor Premises or to terminate
this Sublease. If Tenant elects to proceed, Landlord and Tenant shall negotiate
in good faith the exact areas, length of term, time of access for buildout,
recognition of Tenant by Overlandlord and any mortgagee(s) of Overlandlord and
other matters affecting the Second Floor Premises. Further, if such election to
proceed is made, Tenant agrees to prepare drawings, plans and specifications for
improvements to the Second Floor Premises for Tenant's use and occupancy thereof
for the Permitted Use either prior to or promptly after the closing of the IPO
and to use reasonable efforts to obtain any necessary licenses, permits and
approvals and the approval of the Overlandlord and Landlord thereto, Landlord's
consent not to be unreasonably withheld or delayed. Thereafter, Tenant shall
proceed diligently to construct its improvements and relocate its operations
from the Third Floor Premises to the Second Floor Premises. In the event that
all such matters have not been agreed to and this Sublease modified to
accommodate such matters and as modified, executed and delivered by both parties
on or before three months after the date of the closing of the IPO, either party
shall have the right to terminate this Sublease upon 120 days written notice to
the other.

      In the event that, despite Tenant's efforts, it has not obtained
Overlandlord's consent to such plans and, to the extent required, any
modification to this Sublease arising out of the good faith negotiations
pursuant to this Section 5.2, within 4 months of the date of the closing of the
IPO, then Tenant or Landlord may terminate this Sublease by written notice to
the other setting forth an effective date of termination not less than 90 days
following the date of such notice. This right of termination shall terminate in
the event such Overlandlord's consent is obtained prior to the date any such
notification is given.

      If Tenant has notified Landlord that it elects to proceed as set forth in
the first paragraph of this Section 5.2, Tenant shall have six months after
closing of the IPO to obtain all permits and complete its buildout plus an
additional six months


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so long as construction is in process six months after the date of the closing
of the IPO, plus such further time as Tenant is delayed, day for day, due to
force majeure, up to a maximum of a further six months. If Tenant has not
completed its buildout by such time, Landlord shall have the right to terminate
this Sublease. If Tenant determines it cannot obtain all necessary permits and
approvals, including without limitation, a wastewater discharge permit, within
six months from closing of the IPO it shall so notify Landlord, whereupon either
Landlord or Tenant may within 30 days terminate this Sublease effective 90 days
from the date of the termination notice.

      If Tenant has elected to proceed under this section, Fixed Rent and
Additional Rent for the Second Floor Premises shall be payable commencing on the
Rent Commencement Date--Second Floor and no Fixed Rent or Additional Rent
hereunder shall be due for the Third Floor Premises. Tenant shall vacate the
Third Floor Premises upon occupancy by Tenant of the Second Floor Premises.

      If Tenant elects not to proceed with occupancy and buildout of the Second
Floor Premises, each party shall have the right by 90 days written notice to
terminate this Sublease effective no earlier than 210 days after the date of
closing of the IPO.

      Within a period of 180 days after the execution of this Sublease, Tenant
will use commercially reasonable efforts to accomplish an underwritten initial
public offering of its Common Stock, in which offering Tenant will attempt to
raise between $20 and $30 million (the "IPO"), net to Tenant. Landlord or Tenant
shall be entitled to terminate this Sublease upon 180 days written notice to the
other if the IPO is not consummated on or before January 1, 1997, or, if on
December 31, 1996 Tenant has a registration statement on file with the SEC, and
in Tenant's reasonable judgment, there does not appear to be any material
impediment to the successful completion of the IPO, on or before March 31, 1997.


ARTICLE 6.  OVERLEASE:

      Section 6.1. This Sublease is subject and subordinate to the terms and
conditions of the Overlease. Except as otherwise specifically provided in this
Sublease, Landlord shall be deemed to be landlord under the Overlease, Tenant
shall be deemed to be tenant under the Overlease, and all of the provisions of
the Overlease contained in Exhibit A hereto are incorporated herein by reference
with the same force and effect as if they were fully set forth herein, except
that Tenant shall not have any Expansion Options or Right of First Offer,
Extension Options or right of self-help, and except, further, that the
provisions regarding general and environmental indemnity and the provisions of
Sections 2.6 - 2.12, Section 5.3 (relating to a rent abatement),


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Section 6.8, Section 11.11, Section 11.8 and Exhibit C shall not apply. Landlord
represents and warrants that the attached document is a true, accurate and
complete copy of the Overlease and any amendments or instruments or documents
materially adversely affecting Tenant's occupancy of the Demised Premises
related thereto. Except as otherwise specifically provided in this Sublease,
Tenant agrees from and after the date hereof fully to comply with all of the
terms, conditions and obligations of Landlord as tenant under the Overlease
applicable to the Demised Premises as if Tenant were the tenant thereunder. The
Tenant shall comply with all federal, state and local (including zoning) laws,
regulations, ordinances, executive orders, federal guidelines and similar
requirements in effect from time to time with respect to Tenant's use and
occupancy of the Demised Premises. Tenant shall comply with all conditions of
any and all permits, licenses and other governmental or regulatory approvals
(collectively, "Permits") required for Tenant's use of the Demised Premises,
including, without limitation, the discharge or emission of regulated materials
or wastes. Prior to occupancy of the Second Floor Premises Tenant shall obtain,
and provide a copy to Landlord of, all Permits required for Tenant's business
operations and its use of the Demised Premises and shall consult with Landlord
concerning, and obtain its prior written approval (not to be unreasonably
withheld or delayed) of, any Permits. The Tenant may use the Demised Premises,
and any portion of the Building only for the Permitted use. During the Initial
Term, Tenant shall not conduct any activities nor take any actions, nor permit
any actions to be taken which would require any license, permit or approval not
obtained by Tenant. Without limiting the generality of the foregoing, during the
Initial Term Tenant, unless it obtains all necessary licenses, permits and
approvals, shall not store any flammable or other hazardous materials (which
shall not preclude Tenant from having small quantities of such materials for
normal use in compliance with applicable legal requirements), nor store or
dispose of hazardous waste.

      Tenant shall not cause, nor permit, a default under the Overlease. If the
Overlease terminates before the end of its Term for any reason whatsoever,
including Landlord's default, this Sublease shall also terminate and Landlord
shall have no liability to Tenant arising out of or in connection with such
termination, including without limitation, any damages.

      Landlord represents that as of the date hereof, no material default has
occurred under the Overlease outstanding past applicable cure periods. Landlord
agrees promptly to provide Tenant with a copy of any default notice received by
Landlord from Overlandlord. Landlord, as landlord under this Sublease, shall
have the benefit of all rights, remedies and limitations of liability enjoyed by
Overlandlord as the landlord under the Overlease, but (i) Landlord shall have no
obligations under this Sublease to perform any obligations of Overlandlord, as
landlord,


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under the Overlease (including without limitation any obligations to provide
services, maintain insurance or to perform the Overlandlord's obligations under
Sections 5.1, 5.3, 5.5, 6.2, 10.1 (relating to non-disturbance agreements), 12.1
or 12.5 of the Overlease, (ii) Landlord shall not be bound by any
representations or warranties of Overlandlord as landlord under the Overlease;
(iii) in any case where the consent of Overlandlord is required under the terms
of the Overlease, the consent of Landlord and Overlandlord shall be required and
(iv) Landlord shall not be liable to Tenant for any failure or delay in
Overlandlord's performance of its obligations as landlord under the Overlease.

      Section 6.2. Notwithstanding any contrary provision of this Sublease, (i)
in any instances where Overlandlord, as landlord under the Overlease, has a
certain period of time in which to notify Landlord, as tenant under the
Overlease, whether Overlandlord will or will not take some action, Landlord, as
landlord under this Sublease, shall have an additional ten-day period after
receiving such notice in which to notify Tenant, (ii) in any instance where
Landlord, as tenant under the Overlease, has a certain period of time in which
to notify Overlandlord, as landlord under the Overlease, whether Landlord will
or will not take some action, Tenant, as tenant under this Sublease, must notify
Landlord, as landlord under this Sublease, at least five business days before
the end of such period, but in no event shall Tenant have a period of less than
five days in which so to notify Landlord unless the period under the Overlease
is five days or less, in which case the period under this Sublease shall be two
days less than the period provided to Landlord as Tenant under the Overlease,
and (iii) in any instance where a specific grace or cure period is granted to
Landlord, as tenant under the Overlease, Tenant, as tenant under this Sublease,
shall be deemed to have a grace or cure period, as applicable, which is ten days
less than Landlord, but in no event shall any grace or cure period be reduced to
less than five days unless the period under the Overlease is five days or less,
in which case the period under this Sublease shall be two days less than the
period provided to landlord under the Overlease.

ARTICLE 7.  TENANT'S COVENANTS AND INDEMNITY:

      Section 7.1. Tenant covenants and agrees that Tenant will not do or permit
anything which would constitute or could cause a default under the provisions of
the Overlease or omit to do or permit the omission of anything which Tenant is
obligated to do under the terms of this Sublease which would constitute or could
cause a default under the Overlease. Tenant's use of the Common Areas shall be
at its own risk.

      Section 7.2. To the maximum extent this agreement may be made effective
according to law, the Tenant agrees to indemnify


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and save harmless the Landlord from and against all claims, loss, or damage of
whatever nature to the extent arising from any breach by the Tenant of any
obligation of the Tenant under this Sublease or any negligence or willful
misconduct of the Tenant, or the Tenant's contractors, licensees, invitees,
agents, servants or employees, or arising from any accident, injury or damage
whatsoever caused to any person or property, occurring after the date that
possession of the Demised Premises is first delivered to the Tenant and until
the end of the Term and thereafter, so long as the Tenant is in occupancy of any
part of the Demised Premises, in or about the Demised Premises or arising from
any accident, injury or damage occurring outside the Demised Premises but in or
on the Property, or any other areas within the Buildings or, on the Land (as
defined in the Overlease), to the extent such accident, injury or damage
results, or is claimed to have resulted, from the negligent act or omission or
wilful misconduct on the part of the Tenant or the Tenant's agents or
contractors, licensees, invitees, servants or employees, provided that the
foregoing indemnity shall not include any cost or damage to the extent arising
from any negligent or willful act or omission of the Landlord, or the Landlord's
contractors, licensees, invitees, agents, servants or employees. This indemnity
and hold harmless agreement shall include indemnity against reasonable
attorneys' fees and all other costs, expenses and liabilities incurred or in
connection with any such claim or proceeding brought thereon, and the defense
thereof and shall survive termination or expiration of this Sublease.

      In the event of a default by Tenant in the full and timely payment and
performance of its obligations and covenants under this Sublease, Landlord shall
have all of the rights and remedies in the Overlease with respect to defaults by
the tenant under the Overlease, including without limitation the rights and
remedies set forth in Article 9 of the Overlease. Neither Landlord nor Tenant
shall be responsible for indirect or consequential damages suffered by the
other, regardless of the cause. Tenant shall perform all of its obligations and
agreements under the Master Agreement and a rescission pursuant to Section 8.07
of the Master Agreement shall be deemed to be an Event of Default hereunder.

ARTICLE 8.  LANDLORD'S COVENANTS AND INDEMNITY:

      Section 8.1. Landlord covenants and agrees that Landlord shall not enter
into any modification or other agreement with respect to the Overlease which
would prevent the use by Tenant of the Demised Premises in accordance with the
terms of this Sublease, or which would increase the obligations of Tenant or
increase the Fixed Rent or Additional Rent required to be paid by Tenant under
the terms of this Sublease unless in either case in Landlord's reasonable
opinion, such an amendment to the Overlease will benefit Tenant as well as
Landlord.


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      Section 8.2. To the maximum extent this agreement may be made effective
according to law, the Landlord agrees to indemnify and save harmless the Tenant
from and against all claims, loss, or damage of whatever nature to the extent
arising from any breach by the Landlord or any obligation of the Landlord under
this Sublease or any negligence or willful misconduct of the Landlord, or the
Landlord's contractors, licensees, invitees, agents, servants or employees, or
arising from any accident, injury or damage occurring after the date that
possession of the Demised premises is first delivered to the Tenant and until
the end of the Term and thereafter, so long as the Tenant is in occupancy of any
part of the Demised Premises, in or about the Demised Premises or arising from
any accident, injury or damage occurring outside the Demised Premises but in or
on the Property, or any other areas within the Buildings or, on the Land (as
defined in the Overlease), to the extent such accident, injury or damage
results, or is claimed to have resulted, from the negligent act or omission or
wilful misconduct on the part of the Landlord or the Landlord's agents or
contractors, licensees, invitees, servants or employees, provided that the
foregoing indemnity shall not include any cost or damage to the extent arising
from any negligent or willful act or omission of the Tenant, or the Tenant's
contractors, licensees, invitees, agents, servants or employees. This indemnity
and hold harmless agreement shall include indemnity against reasonable
attorneys' fees and all other costs, expenses and liabilities incurred or in
connection with any such claim or proceeding brought thereon, and the defense
thereof and shall survive termination or expiration of this Sublease.

ARTICLE 9.  PERFORMANCE BY OVERLANDLORD:

      Section 9.1. It is understood and agreed that Landlord shall at all times
use reasonable efforts to seek to obtain compliance by Overlandlord with all of
its Obligations under the Overlease that affect Tenant.


ARTICLE 10.  BROKERAGE REPRESENTATIONS:

      Section 10.1. Landlord represents to Tenant that it has engaged no broker
in consummating the transaction contemplated by this Sublease. Tenant represents
to Landlord that it has engaged no broker in consummating the transaction
contemplated by this Sublease. Landlord and Tenant each agree to indemnify and
hold the other harmless from and against any and all loss, cost, damage or
expense (including without limitation reasonable attorneys' fees) arising out of
or incurred in connection with any breach or claimed breach of its
representation contained in the two preceding sentences.


                                    - 12 -
<PAGE>   13
ARTICLE 11.  NOTICES:

      Section 11.1. Any bill or notice by Landlord to Tenant shall be deemed
sufficiently given if such bill or notice is in writing and is delivered to
Tenant's authorized agent Attn: President at the Demised Premises with copies to
Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., One Financial Center,
Boston, Massachusetts 02111, Attention: Joel R. Bloom or deemed given when first
refused or when delivered by registered or certified United States mail, return
receipt requested, addressed to Tenant at the Demised Premises, or at such other
address as Tenant shall specify to Landlord.

      Section 11.2. Any notice by Tenant to Landlord shall be deemed sufficient
given if such notice is in writing and is delivered to Landlord at the Building
Attention: General Counsel, with copies to: Testa, Hurwitz & Thibeault, 125 High
Street, Boston, Massachusetts, 02100, Attention: Margaret W. Brill or deemed
given when first refused or when delivered by registered or certified United
States mail, return receipt requested, addressed to Landlord at the Buildings,
or in each case at such other address as Landlord shall specify to Tenant.

ARTICLE 12.  FURTHER SUBLEASE OR ASSIGNMENT:

      Section 12.1. Tenant covenants and agrees that neither this Lease nor the
term and estate hereby granted, nor any interest herein or therein, will be
assigned, sublet, mortgaged, pledged, encumbered or otherwise transferred,
voluntarily or by operation of law or otherwise, without the prior written
consent of Landlord which may be withheld, granted or conditioned in its sole
discretion, and, if required under the Overlease, Overlandlord. An acquisition
of Tenant by a PerSeptive Competitor, or a Change of Control in which a
PerSeptive Competitor shall come to control Tenant, as such terms are defined in
and as further described in Section 9.4 of the License Agreement, shall be
deemed to be an assignment of this Sublease requiring Landlord's consent in its
sole discretion as described in the preceding sentence. A merger or
consolidation, or a sale of all or substantially all of the stock, assets or
business of Tenant and its subsidiaries taken as a whole, shall also be deemed
to be an assignment of this Sublease but Landlord's consent in such case shall
not be unreasonably withheld or delayed. Reasonable consent shall be determined
consistent with the provisions of Section 6.8 of the Overlease, but excluding
its provisions concerning recapture and sharing of profits.

ARTICLE 13.  ACCESS:

      Section 13.1. Landlord and Overlandlord shall have the right to enter and
examine the Demised Premises in accordance with and for the purposes set out in
Section 6.5 of the Overlease


                                    - 13 -
<PAGE>   14
and also, to remove, at Tenant's expense, any changes and additions installed by
Tenant and not consented to by Landlord and, if required, Overlandlord, in
writing. Landlord shall also have the right to enter the Demised Premises for
purposes contemplated by the Consulting and Services Agreement between Landlord
and Tenant, and any other Related Agreement, and, in any event, if Tenant has
given its consent thereto. In addition, during the last six (6) months prior to
the end of the then Term and at any time Tenant is in default under the terms of
this Sublease beyond applicable notice and cure periods, Landlord and Landlord's
representatives may enter the Premises to show the Premises to prospective
subtenants, provided that Landlord shall use reasonable efforts to minimize
disruption to Tenant's business operations. Landlord agrees to give Tenant a
list of the names of all persons authorized by Landlord to show the Premises to
prospective subtenants, and, subject to the Overlandlord's rights under the
Overlease, shall comply with all of Tenant's reasonable security and/or
confidentiality measures and procedures.

ARTICLE 14.  SIGNAGE:

      Section 14.1. Tenant shall be entitled, at Tenant's cost and in compliance
with all codes, ordinances and regulations, to install signs in and on the
Premises and Building with Landlord's consent, not to be unreasonably withheld
or delayed, subject to Overlandlord's consent.


ARTICLE 15. DEFAULT:

      Section 15.1. Without limiting the generality of Section 6.1, Article 9 of
the Overlease is incorporated as though set forth herein, subject to
modification by the terms of Section 6.2 hereof.


                                    - 14 -
<PAGE>   15
ARTICLE 16.  ESTOPPEL CERTIFICATE:

      Section 16.1. Provided that the following conditions and facts are
determined by the Tenant to be true, Tenant agrees from time to time hereafter,
upon not less than ten (10) days' prior written request by Landlord or
Overlandlord, to execute, acknowledge and deliver to Landlord or Overlandlord a
statement in writing certifying that this Sublease is unmodified and in full
force and effect; that Tenant has no defenses, offsets or counterclaims against
its obligations to pay the Fixed Rent, Additional Rent and other amounts due
hereunder and to perform its other covenants under this Sublease; that there are
no uncured defaults of Landlord or Tenant under this Sublease (or, if there are
any modifications, defenses, offsets, counterclaims, or defaults, setting them
forth in reasonable detail); and the dates to which the Fixed Rent, Additional
Rent and other charges have been paid. Any such statements delivered pursuant to
this Section may be relied upon by Landlord and any other party to whom the
statement, at Landlord's or Overlandlord's request, is addressed.

ARTICLE 17.  MISCELLANEOUS PROVISIONS:

      Section 17.1. During the Sublease term, Tenant shall maintain insurance of
such types, in such policies, with such endorsements and coverages, and in such
amounts as are set forth in Article 7 of the Overlease, and such additional
insurance as may be required by Landlord, in Landlord's reasonable discretion.
All insurance policies shall name Overlandlord and Landlord as additional
insureds and loss payees and shall contain an endorsement that such policies may
not be modified or canceled without 30 days prior written notice to Overlandlord
and Landlord. Tenant shall promptly pay all insurance premiums and shall provide
Overlandlord and Landlord with policies or certificates evidencing such
insurance.

      Section 17.2. This Sublease may be amended or modified only by written
instruments executed by both Landlord and Tenant.

      Section 17.3. This Sublease, and the rights and obligations of Landlord
and Tenant under this Sublease, are subject to the condition that Overlandlord
consent to this Sublease, and this Sublease shall be effective only upon the
receipt by Landlord and Tenant of such consent (the "Overlandlord Consent
Date"). In the event the Overlandlord Consent Date shall not have occurred on or
before August 15, 1996, then, Landlord and Tenant shall each have the option to
terminate this Sublease by 30 days written notice thereof to the other.

      Section 17.4. Except to the extent caused by the negligence, wilful
misconduct or failure of Landlord to comply with its obligations and covenants
set forth in this Sublease or


                                    - 15 -
<PAGE>   16
in any other agreement between Landlord and Tenant, the Tenant shall indemnify
and hold the Landlord, and its agents, servants, employees, officers, directors,
partners, beneficiaries and trustees, harmless from and against any and all
actions, petitions, orders, claims or demands made, brought or instituted by any
and all private parties and/or any and all public agencies or authorities,
together with any and all reasonable expenses, including reasonable attorney's
fees, costs, losses, demands, liabilities, fines or penalties assessed against
or incurred by any of them, including, without limitation, any of the foregoing
arising under CERCLA, similar state laws, other statutes or common law cause of
action imposing liability without regard to fault arising out of or in any way
connected with any loss or damage to persons or property resulting from the
introduction, generation, storage, disposal, seepage, leakage or release of
Hazardous Material (as defined in the Overlease) into the Demised Premises by
the Tenant, its agents, servants, employees or contractors, or from the improper
release of Hazardous Materials anywhere on the Property by, for or on behalf of
the Tenant.

      Section 17.5. Except to the extent caused by the negligence, wilful
misconduct or failure of Tenant to comply with its obligations and covenants set
forth in this Sublease or in any other agreement between Landlord and Tenant the
Landlord shall indemnify and hold the Tenant, and its agents, servants,
employees, officers, directors, partners, beneficiaries and trustees, harmless
from and against any and all actions, petitions, orders, claims or demands made,
brought or instituted by any and all private parties and/or any and all public
agencies or authorities, together with any and all reasonable expenses,
including reasonable attorney's fees, costs, losses, demands, liabilities, fines
or penalties assessed against or incurred by any of them, including, without
limitation, any of the foregoing arising under CERCLA, similar state laws, other
statutes or common law cause of action imposing liability without regard to
fault arising out of or in any way connected with any loss or damage to persons
or property resulting from the introduction, generation, storage, disposal,
seepage, leakage or release of Hazardous Material (as defined in the Overlease)
into the Demised Premises by the Landlord, its agents, servants, employees or
contractors, or from the improper release of Hazardous Materials anywhere on the
Property by, for or on behalf of the Landlord.


                                    - 16 -
<PAGE>   17
      IN WITNESS WHEREOF, the parties hereto have caused this Sublease to be
duly executed under seal as of the day and year first above written.

                                    PERSEPTIVE BIOSYSTEMS, INC.



                                    BY: /s/ Noubar Afeyan
                                       -----------------------------------


                                    CHEMGENICS PHARMACEUTICALS INC.



                                    BY: /s/ Barry Berkowitz
                                       -----------------------------------



                                    - 17 -
<PAGE>   18
                                   EXHIBIT A

      The Lease dated May 24, 1994 between 500 Old Connecticut Path Limited
Partnership as Landlord and PerSeptive Biosystems, Inc. as Tenant is attached
hereto and incorporated herein by reference.


                                    - 18 -
<PAGE>   19
                                   EXHIBIT B

                           PLANS OF DEMISED PREMISES
                        AND DESCRIPTION OF COMMON AREAS

                                  (ATTACHED)





                                    - 19 -