FIRST AMENDMENT TO SALE-PURCHASE AGREEMENT

     THIS FIRST AMENDMENT TO SALE-PURCHASE AGREEMENT (this "Amendment"), dated
October 30, 1998, by and between SOUTH MIDDLESEX INDUSTRIAL PARK ASSOCIATES,
L.P., a New Jersey limited partnership ("SMIPA") and SM MONROE ASSOCIATES, L.P.,
a New Jersey limited partnership ("SMMA"), each having an office at c/o The
Taylor Simpson Group, One Rockefeller Plaza, New York, New York 10020 (SMIPA and
SMMA are, collectively, "Seller"), and COPT ACQUISITIONS, INC., a Delaware
corporation, having an office at c/o Corporate Office Properties Trust, 401 City
Avenue, Suite 615, Bala Cynwyd, Pennsylvania 19004-1126 ("Purchaser").

                              W I T N E S S E T H :

     WHEREAS, Seller and Purchaser have entered into that certain Sale-Purchase
Agreement (the "Contract"), dated as of August 20, 1998, pursuant to which
Seller agreed to sell to Purchaser and Purchaser agreed to purchase from Seller
eleven properties located in the Township of South Brunswick and the Township of
Monroe, County of Middlesex and State of New Jersey, as more particularly
described in Schedule "1" annexed to and made a part of the Contract; and

     WHEREAS, Seller and Purchaser desire to amend the terms of the Contract as
more particularly set forth below.

     NOW, THEREFORE, in consideration of the mutual covenants and conditions set
forth in the Contract and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Seller and Purchaser hereby agree
as follows:

     1. All capitalized terms used but not defined herein shall have the
meanings ascribed to them in the Contract.

     2. The Warehouse Properties, to wit, those properties known as 1 South
Middlesex Avenue, 21 Commerce Drive and 40 Commerce Drive, located in Middlesex
County, New Jersey, and all Land, Buildings, Personal Property and other rights
and interests of Seller in respect of the Warehouse Properties (collectively,
the "Excluded Properties") shall be excluded from the Premises which are the
subject of the sale contemplated under the Contract. In furtherance of the
foregoing (a) Schedule "1" of the Contract shall be deleted therefrom and
Schedule "1" annexed hereto (with the metes and bounds descriptions therefor)
shall be inserted in lieu thereof and (b) wherever the term "Individual
Properties" appears in the Contract, it shall mean the Office Properties and the
Flex Properties, exclusive of the Warehouse Properties.

     3. Section 4(a) of the Contract shall be amended as follows:

        (a) the Due Diligence Period, as described in clause (i), is hereby
terminated; and

        (b) Purchaser's right to terminate the Contract during the Due
Diligence Period is void and of no further effect.




     4. (a) Section 4(b) of the Contract shall be amended so that the Closing
Date shall be 10:00 a.m. on Thursday, October 30, 1998. All other provisions of
Section 4(b) shall be applicable to the Closing Date.

        (b) Concurrently upon the execution and delivery of this Amendment by 
and between Seller and Purchaser, Purchaser shall deliver to the Escrow Agent 
the amount of ONE MILLION AND 00/100 ($1,000,000) DOLLARS (the "Supplemental 
Downpayment"), by a bank wire transfer, intrabank transfer, or other 
electronic transfer of immediately available funds to an account designated 
by Escrow Agent, which amount shall be held in escrow by Escrow Agent in the 
same manner as the Downpayment is required to be held under the Contract and 
shall be deemed to be part of such Downpayment. Purchaser shall cause Escrow 
Agent to send Seller written notice via telecopier confirming receipt of the 
Supplemental Downpayment. If (x) the Supplemental Downpayment is not paid by 
Purchaser to the Escrow Agent as aforesaid or (y) such notice is not received 
by Seller within two (2) business days after the execution and delivery of 
this Agreement, Seller may terminate this Agreement effective upon the 
sending of notice to Purchaser by telecopier (notwithstanding the notice 
provisions of Section 23) or as otherwise provided in Section 23, whereupon 
the Downpayment, and Supplemental Downpayment (if Purchaser shall have 
delivered the Downpayment and Supplemental Downpayment to Escrow Agent), 
shall be returned to Purchaser. Notwithstanding the foregoing provisions of 
this Paragraph 4(b), the termination right of Seller set forth in the 
immediately preceding sentence, and Purchaser's obligation to deliver the 
Supplemental Downpayment, shall be void and of no effect if the Closing shall 
occur during the two (2) business day period referenced in such sentence. If 
the Closing shall occur, Seller shall be entitled to receive the Downpayment 
and Supplemental Downpayment, and all interest accrued thereon, if any, and 
such interest shall be credited against the portion of the Purchase Price 
payable pursuant to Section 2(b) of the Contract.

     5. Section 2 of the Contract shall be amended so that the Purchase Price
shall be THIRTY-ONE MILLION TWO HUNDRED FIFTY THOUSAND AND 00/100
($31,250,000.00) DOLLARS, subject to adjustment as provided herein and in the
Contract.

     6. (a) At Closing, Seller shall deliver to Purchaser a lease agreement in
the form annexed hereto as Exhibit "A" (the "Substitute Lease") pursuant to
which Seller shall lease from Purchaser certain premises to be designated by
Purchaser on the second floor of 104 Interchange Plaza (the "Substitute Space"),
which lease shall provide, inter alia, as follows: (i) upon delivery of the
lease to Purchaser, Seller shall deposit with Purchaser the aggregate amount of
$268,521 which shall be held by Purchaser as security in respect of the
obligation to pay base rent under the Substitute Lease; (ii) Purchaser, as
landlord under the Substitute Lease, shall be entitled to draw upon said
security in equal monthly installments on the first (1st) of each month during
the nine (9) month period immediately following the Closing (it being understood
that if the Closing occurs on a date other than the first (1st) of the month
Purchaser shall be entitled to draw a pro rated amount at the Closing in respect
of the remaining portion of the month in which the Closing occurs); (iii) except
for such right to draw upon such security as set forth in the preceding clause
(ii), Purchaser shall have no right to receive from Seller, and Seller shall
have no obligation to pay Purchaser, any payment of base rent, additional rent
or any other amount whatsoever (other than as expressly set forth in the
parenthetical exception in clause (vi) below) in respect of the Substitute Lease
or the Substitute Space, it being expressly agreed that Seller's sole obligation
(other than as expressly set forth in the 


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parenthetical exception in clause (vi) below) in respect of the Substitute Space
and the Substitute Lease shall be to deposit the security with Purchaser as
described in clause (i) above; (iv) the Substitute Lease shall expire and be of
no further force and effect upon the earlier of (x) nine (9) months from the
date thereof, or (y) the effective date of termination of the Substitute Lease
as set forth in written notice from Purchaser to Seller, or (z) at such time as
Purchaser shall receive the aggregate amount of $268,521 from Seller, or from
any party which now is or hereafter becomes obligated to pay rent in respect of
the Substitute Space (or any of such party's affiliates), in respect of base
rent attributable to the Substitute Space during the remaining term of the
Substitute Lease; (v) Purchaser shall obtain and maintain during the term of the
Temporary Lease, comprehensive general liability insurance in the amount of at
least $5,000,000 combined single limit per occurrence and in the aggregate
naming Seller as additional insured; and (vi) Purchaser shall indemnify Seller
for any and all liability whatsoever (including, without limitation, reasonable
attorneys fees and disbursements) which Seller may incur in respect of the
Substitute Space and the Substitute Lease after the Closing (except to the
extent caused by Seller at the Premises during its possession thereof), it being
understood and agreed that the delivery of the Substitute Lease by Seller to
Purchaser is an accommodation to Purchaser and that the parties intend that
Seller shall have no liability whatsoever in connection therewith except for the
payment of security as aforesaid; and (vii) if, upon the expiration or
termination of the Substitute Lease, there shall be any remaining security held
by Purchaser under the Substitute Lease, it shall remit same to Seller within
ten (10) days after such expiration or termination. The provisions of this
paragraph 6(a) shall survive the Closing.

        (b) At Closing, Seller shall deliver to Purchaser a lease agreement in 
the form annexed hereto as Exhibit "B" (the "SSI Lease") pursuant to which 
Seller shall lease from Purchaser certain premises located at, on or 
proximate to 47 Commerce Drive to be designated by Purchaser (the "SSI 
Space"), which lease shall provide, inter alia, as follows: (i) upon delivery 
of the lease to Purchaser, Seller shall deposit with Purchaser the aggregate 
amount of $81,386 which shall be held by Purchaser as security in respect of 
the obligation to pay rent under the SSI Lease; (ii) Purchaser, as landlord 
under the SSI Lease, shall be entitled to draw upon said security in equal 
monthly installments on the first (1st) of each month during the twelve (12) 
month period immediately following the Closing (it being understood that if 
the Closing occurs on a date other than the first (1st) of the month 
Purchaser shall be entitled to draw a pro rated amount at the Closing in 
respect of the remaining portion of the month in which the Closing occurs); 
(iii) except for such right to draw upon such security as set forth in the 
preceding clause (ii), Purchaser shall have no right to receive from Seller, 
and Seller shall have no obligation to pay Purchaser, any payment of base 
rent, additional rent or any other amount whatsoever (other than as expressly 
set forth in the parenthetical exception in clause (vi) below) in respect of 
the SSI Lease or the SSI Space, it being expressly agreed that Seller's sole 
obligation (other than as expressly set forth in the parenthetical exception 
in clause (vi) below) in respect of the SSI Space and the SSI Lease shall be 
to deposit the security with Purchaser as described in clause (i) above; (iv) 
the SSI Lease shall expire and be of no further force and effect upon the 
earlier of (x) twelve (12) months from the date thereof, or (y) the effective 
date of termination of the SSI Lease as set forth in written notice from 
Purchaser to Seller, or (z) at such time as Purchaser shall receive, from 
Somfy Systems, Inc. the first payment of increased base rent resulting from 
the expansion of its premises pursuant to Amendment No. 2 dated March 1, 
1998; (v) Purchaser shall obtain and maintain during the term of the 
Temporary Lease, comprehensive general liability insurance in the amount of 
at least $5,000,000 combined single limit per occurrence and in the aggregate 
naming Seller as additional insured; and (vi) Purchaser shall indemnify 
Seller for any and 


                                       3


all liability whatsoever (including, without limitation, reasonable attorneys 
fees and disbursements) which Seller may incur in respect of the SSI Space 
and the SSI Lease after the Closing (except to the extent caused by Seller at 
the Premises during its possession thereof), it being understood and agreed 
that the delivery of the SSI Lease by Seller to Purchaser is an accommodation 
to Purchaser and that the parties intend that Seller shall have no liability 
whatsoever in connection therewith except for the payment of security as 
aforesaid; and (vii) if, upon the expiration or termination of the SSI Lease, 
there shall be any remaining security held by Purchaser under the SSI Lease, 
it shall remit same to Seller within ten (10) days after such expiration or 
termination. The provisions of this paragraph 6(b) shall survive the Closing.

     7. The Acceptable Agreements referenced in Section 11(c) of the Contract,
being those Contracts which Seller shall assign to Purchaser and which Purchaser
shall assume at the Closing pursuant to Assignment and Assumption of Licenses
and Acceptable Agreements, are listed in Schedule "2" annexed hereto.

     8. In no event shall Purchaser or any of its agents, employees or
contractors, or any person or entity affiliated in any manner with any of the
foregoing, be permitted at any time after the Closing to derive any income from
any use of the name "CenterPoint at 8A", it being understood that such name is
and shall remain the sole property of Seller and Seller shall suffer irreparable
harm in connection with any such use. The foregoing shall not preclude Purchaser
from using, free of charge, the name "CenterPoint at 8A" in describing the
location of the Premises (i) on letterhead or in any other business materials
used by Purchaser; or (ii) in marketing or promotional materials in respect of
the Premises (including, without limitation, such materials as may be given to
prospective tenants and purchasers of the Premises). The provisions of this
Paragraph 8 shall survive the Closing.

     9. (a) At the Closing, Seller shall deliver to and deposit with the Title
Company, as escrow agent (the Title Company, in its capacity as escrow agent
hereunder, is hereinafter referred to as the "Escrow Agent"), the following sums
(the "Escrowed Funds"), which amounts shall be segregated and maintained by the
Escrow Agent in separate accounts:

            (i) ONE MILLION THREE HUNDRED THOUSAND AND 00/100 ($1,300,000.00)
                DOLLARS, in respect of costs and expenses (including, without
                limitation, all hard and soft costs relating to construction,
                all commissions and other compensation due to brokers or others
                and all legal, architectural, engineering and other professional
                costs) (collectively, the "Somfy Costs") associated with the
                proposed expansion of 47 Commerce Drive which is currently
                occupied by Somfy Systems, Inc. ("SSI"), as referred to in
                Schedule "9" of the Contract (the "Somfy Expansion"), which sum
                shall be held by the Escrow Agent in accordance with the terms
                of the Escrow Joinder among Seller, Purchaser and Escrow Agent
                annexed hereto and made a part hereof as Exhibit "C." Purchaser
                shall maintain reasonably detailed books and records with
                respect to all monies expended by Purchaser in connection with
                the Somfy Expansion so that the amount and nature of all of such
                expenditures are readily identifiable. Seller shall be entitled
                to inspect such books and records


                                       4


               of Purchaser in the manner prescribed by Section 22(a) of the
               Contract. It is expressly agreed that Seller shall have no
               obligation or liability whatsoever for any Somfy Costs incurred
               at any time by Purchaser or any of Purchaser's affiliates,
               agents, employees, contractors and/or subcontractors, whether or
               not the Somfy Costs shall exceed the amount set forth above in
               this clause (i), it being further expressly agreed that Purchaser
               shall be solely responsible for the Somfy Expansion and all Somfy
               Costs of whatever nature and whenever incurred and that Purchaser
               shall and does indemnify and hold harmless Seller from and
               against all liability arising out of the acts or omissions of
               Purchaser, it agents, employees, contractors or affiliates in
               respect of the Somfy Expansion and the Somfy Costs. Within five
               (5) business days after Seller's written request therefor,
               Purchaser shall give Seller written notice as to (x) whether or
               not SSI has taken occupancy of all or part of the expanded space
               which is the subject of the Somfy Expansion, and/or (y) the date
               of substantial completion of the Somfy Expansion. In no event
               shall Purchaser use any of the funds referenced in this clause
               (i) to pay Somfy Costs to any party which is an affiliate of
               Purchaser except to the extent the amount payable to such party
               does not exceed the reasonable and customary charges in the
               industry for the work or materials in question.

          (ii) ONE HUNDRED SIXTY-EIGHT THOUSAND FIVE HUNDRED NINETY SEVEN AND
               00/100 ($168,597.00) DOLLARS, in respect of the obligation on the
               part of Matrix Realty, Inc. ("Matrix") to pay base rent pursuant
               to a certain Lease Agreement between SMIPA, as lessor, and
               Matrix, as lessee (the "Matrix Lease"), for certain premises
               located at 3 Centre Drive, which sum shall be held by the Escrow
               Agent in accordance with the terms of the Escrow Joinder among
               Seller, Purchaser and Escrow Agent annexed hereto and made a part
               hereof as Exhibit "D."

         (iii) ONE HUNDRED FIFTEEN THOUSAND AND 00/100 ($115,000.00) DOLLARS in
               respect of certain discrepancies in the calculation of closing
               adjustments pertaining to (A) security deposits, (B) operating
               expense escalation payments under Leases and (C) prepaid rents,
               which discrepancies the parties intend to resolve in good faith,
               with appropriate payments out of such funds to be made to Seller
               or Purchaser, as the case may be, within sixty (60) days from the
               Closing. The foregoing sum shall be held by the Escrow Agent in
               accordance with the terms of the Escrow Joinder among Seller,
               Purchaser and Escrow Agent annexed hereto and made a part hereof
               as Exhibit "J".


                                       5


        (b) The Escrowed Funds shall be allocated and funded from the 
Purchase Price and shall be delivered to the Escrow Agent at the Closing and 
maintained in interest bearing accounts or money market funds in Jefferson 
Bank, Philadelphia, Pennsylvania in which the principal balances do not 
fluctuate in value, it being expressly understood that Purchaser shall be 
solely responsible to replace promptly any portion of the principals of any 
of the Escrowed Funds which are reduced due to investment loss or otherwise.

        (c) The provisions of this Paragraph 9 and Exhibits C and D shall
survive the Closing.

    10. Section 26 of the Contract is hereby deleted in its entirety.

    11. Purchaser shall have no obligation to deliver at the Closing any such
easements as are described in Section 27(b) of the Contract.

    12. (a) Seller shall deliver to the Title Company at the Closing a title
affidavit in the form annexed hereto as Exhibit "E".

        (b) Seller shall deliver to Purchaser at the Closing a letter from
Bollerman Real Estate Services in the form annexed hereto as Exhibit "G".

    13. At the Closing, Seller shall deliver to Purchaser, to the extent in
Seller's possession and control and not located at the Premises, (a) the form
lease used by Seller at the Premises (both in hard paper copy and on computer
disk) and (b) Seller's management records located at the Premises with respect
to the billing of rent and additional rent to tenants at the Premises,
including, without limitation, (i) annual reconciliation of estimated additional
rent charges for 1997; (ii) the latest available year-to-date expense statements
for the Individual Properties; and (iii) property management budgets for the
Individual Properties for each of 1997 and 1998.

    14. Section 3(h) of the Contract shall be amended as follows:

        (a) by amending and restating the first sentence of clause (i) 
thereof to read as follows: "Seller shall be responsible for all commissions 
pertaining to Leases entered into prior to the Closing without regard to 
whether the same shall be payable before or after the Closing.";

        (b) by adding the following at the end of clause (i): "At the 
Closing, Seller shall furnish to Purchaser evidence of payment of all 
commissions for which Seller is responsible under this clause (i).";

        (c) Section 3(h)(ii) shall be deleted and the following shall be
inserted in lieu thereof:

            "With respect to Leases, Purchaser shall be responsible for (1)
            the payment of the entire amount of those leasing commissions (x)
            that accrue and become due and owing subsequent to Closing and
            (y) which are required to be paid by the owner pursuant to the
            commission agreements specifically listed on Exhibit "F" attached


                                       6


            hereto and (2) the payment of leasing commissions other than
            those payable pursuant to such agreements with respect to Leases
            to the extent such other leasing commissions (A) accrue and
            become due and owing subsequent to the Closing and (B) do not
            exceed five (5%) percent of the total base rent due under any
            particular lease in question, it being agreed that any such
            commissions in excess of such amount shall be the sole
            responsibility of Seller, which obligation shall survive the
            Closing. The foregoing provision of this Paragraph 3(h)(ii) shall
            be without limitation to Seller's obligations under Paragraph
            3(h)(i). Purchaser agrees to indemnify and hold Seller and
            Seller's Affiliates harmless from any and all claims, demands,
            causes of action, losses, damages, liabilities, and costs and
            expenses (including, without limitation, reasonable attorney's
            fees and disbursements), suffered or incurred by Seller or any of
            Seller's Affiliates arising out of or in connection with claims
            for any commissions which are Purchaser's responsibility to pay
            under this Paragraph 3(h)(ii)."; and

        (d) The following shall be added as new Section 3(h)(iii):

            "(iii) The provisions of this Paragraph 3(h) shall survive the
            Closing."

    15. Section 10(a) of the Contract shall be amended by adding the following
clauses (v) and (vi):

        "(v) Seller shall execute and deliver to Purchaser an easement, in the
    form annexed hereto as Exhibit "H", granting Purchaser, as owner of 101
    Interchange Plaza (Master Plan Parcel 24), the right to use the existing
    sanitary sewer line, if any, located on Master Plan Parcel 35 (Block 8.01;
    Lot 3.012).

        "(vi) Seller shall execute and deliver to Purchaser an easement, in
    the form annexed hereto as Exhibit "I", granting Purchaser, as owner of 104
    Interchange Plaza (Master Plan Parcel 34), the right to drain water into
    that certain fifty foot drainage easement located on Master Plan Parcel 25
    (Block 8; Lot 3.013).

    16. To the extent that Seller or any of its affiliates, under a recorded
Deed of Declaration Protective Covenants (or deed restriction, restrictive
covenant, or other like instrument) affecting the Premises, has the right
pursuant thereto to approve any matter affecting the Premises from and after the
Closing during the period of Purchaser's ownership thereof, Seller shall render
its approval or disapproval in good faith and on a reasonable basis in the
context of the overall development of the properties affected by such Deed of
Declaration Protective Covenants (or deed restriction, restrictive covenant, or
other like instrument) including, without limitation, the development of such
properties which are owned by Seller and or its affiliates.

    17. In the event of any conflict or inconsistency between any provision of
the Contract and any provision of this Amendment, the provisions of this
Amendment shall govern and control.


                                       7


    18. Except as amended hereby, the Contract is hereby reinstated and
affirmed and shall continue unmodified and in full force and effect.

    IN WITNESS WHEREOF, this Amendment has been duly executed by the parties
hereto as of the day and year first above written.


ATTEST:                                  SELLER:


                                         SOUTH MIDDLESEX INDUSTRIAL
                                          PARK ASSOCIATES, L.P.

                                         By:      MR Realty Associates, L.P.,
                                                  General Partner

                                         By:      Rockmid Realty, Inc.,
                                                  General Partner

                                         By: /s/ Henry R. Taylor
- ----------------------------                -------------------------
         Secretary                          Henry R. Taylor,
                                            Vice President


                                         SM MONROE ASSOCIATES, L.P.

                                         By:      SM Associates, L.P.,
                                                  General Partner

                                         By:      Monroe Realty, Inc.,
                                                  General Partner


                                         By: /s/ Henry R. Taylor
- ----------------------------                -------------------------
         Secretary                          Henry R. Taylor,
                                            Vice President


                                      8



ATTEST:                                  PURCHASER:


                                         COPT ACQUISITIONS, INC.,
                                         Purchaser

                                         By:
- ----------------------------                -------------------------
         Secretary                          Clay W. Hamlin, III,
                                            President


Solely for the purpose of agreeing to
Section 9 of this Amendment and the
provisions of the Escrow Joinder
Agreements, annexed hereto as Exhibits C
and D.



COMMONWEALTH LAND TITLE INSURANCE COMPANY


By:
   --------------------------------------
   Name:
   Title:


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