FIRST AMENDMENT TO PURCHASE AND SALE AGREEMENT



                  THIS FIRST  AMENDMENT  TO PURCHASE  AND SALE  AGREEMENT  (this
"Amendment")  is made as of October 1, 2002, by and between CENTRE SQUARE TWO, a
Pennsylvania general partnership  (hereinafter  sometimes referred to as "Ground
Lessor"),  and CENTRE SQUARE, a Pennsylvania  general  partnership  (hereinafter
sometimes referred to as "Ground Lessee";  Ground Lessor and Ground Lessee being
hereinafter  collectively  sometimes referred to "Seller"),  and HRPT PROPERTIES
TRUST, Maryland Real Estate Investment Trust ("Purchaser").



                              W I T N E S S E T H:



                  A. Seller and  Purchaser  executed  that certain  Purchase and
Sale Agreement dated as of September 30, 2002 (the "Agreement").


                  B. Purchaser's Title Inspection Period and Inspection  Period,
as such terms are defined in the Agreement,  expired at 5:00 p.m. EDT on October
1, 2002.


                  C. Based upon  Purchaser's  due  diligence  within  said Title
Inspection Period and Inspection Period, Purchaser has identified certain items,
as further set forth in the attached Exhibit A (the "Due Diligence Issues") that
have resulted in Purchaser's request of a reduction in the Purchase Price.


                  D. Seller is willing to amend the Closing  date in  accordance
with the terms and conditions set forth herein.


                  E. All terms  not  otherwise  defined  herein  shall  have the
meaning set forth in the Agreement.



         NOW, THEREFORE, in consideration of Ten dollars ($10.00) and other good
and valuable consideration,  receipt of which is hereby acknowledged,  Purchaser
and Seller hereby agree as follows:



                  1.  Purchaser  agrees that it will  deposit  the Deposit  with
Escrow  Agent in  accordance  with the terms  and  conditions  contained  in the
Agreement.


                  2.  Seller  agrees that it will  discuss  with  Purchaser  and
evaluate  Purchaser's  request for a reduction in the Purchase Price as a result
of the Due Diligence Issues.


                  3.  Purchaser  and Seller  agree that the Closing date will be
extended  one (1) week from  October 3, 2002 to October 10,  2002 (the  "Revised
Closing Date").


                  4. If  Purchaser  and Seller are unable to agree on a Purchase
Price or to  otherwise  reach an  agreement  with  respect to the Due  Diligence
Issues,  Purchaser shall have the option to terminate the Agreement upon written
notice to Seller,  which  notice  shall be delivered to the parties set forth in
paragraph 10.4 of the Agreement by personal  delivery,  or by legible  facsimile
transmission,  no later  than 5:00 pm EDT on  October  9,  2002,  whereupon  the
Agreement shall terminate,  the Deposit shall be returned to the Purchaser,  and
neither party shall have any further rights or obligations hereunder (except for
any indemnity  obligations of either party  pursuant to the other  provisions of
the Agreement).  In the event Purchaser does not send such notice of termination
to Seller by said date and time, or the parties do not otherwise reach agreement
in writing to a reduction in the Purchase  Price on account of the Due Diligence
Issues,  the  Agreement  shall remain in full force and effect and Purchaser and
Seller  shall  proceed  with the  Closing on the  Revised  Closing  Date with no
reduction in the Purchase Price.


                  5. Except as  specifically  amendment by this  Amendment,  the
Agreement shall remain in full force and effect.


                  6.  This   Amendment   may  be   executed  in  any  number  of
counterparts,  each of which shall be deemed an original,  but such counterparts
shall together  constitute one and the same agreement.  Any such counterpart may
be delivered by facsimile





                            (Signatures Pages Follow)







                  IN WITNESS WHEREOF, the parties have hereto duly executed this
Amendment as of the date above written.

SELLER:

CENTRE SQUARE TWO, a Pennsylvania general partnership, by
its authorized general partner, Centre Square Three, by its
authorized general partner, Centre Square Five, by its authorized
general partner, Metropolitan Life Insurance Company


By: /s/ Amy S. Hersh
        Amy S. Hersh, Director

CENTRE SQUARE, a Pennsylvania general partnership, by its
authorized general partner, Metropolitan Life Insurance
Company


By: /s/ Amy S. Hersh
        Amy S. Hersh, Director


PURCHASER:

HRPT PROPERTIES TRUST,
a Maryland real estate investment trust


By:   /s/ John Mannix

Name: John Mannix

Title: President