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                                                                   EXHIBIT 10.21

                        AMENDMENT TO LETTER OF EMPLOYMENT

         THIS AMENDMENT TO LETTER OF EMPLOYMENT ("Amendment") is made and
entered into by and between NEIL E.  WAISNOR ("Employee") and CABOT INDUSTRIAL
PROPERTIES, L.P. ("Employer").

         WHEREAS, Employee and Employer entered into an amended letter of
employment, effective September 10, 1998, which letter of employment was further
amended, effective October 28, 2001 (the "Letter of Employment"), under which
Employee is to receive certain benefits if Employee's employment is terminated
under certain circumstances following a Change in Control (as defined therein)
(the "Change in Control Benefits"); and

         WHEREAS, pursuant to the terms of the Agreement and Plan of Merger,
dated as of October 28, 2001 (the "Merger Agreement"), Cabot Industrial Trust
("REIT") and Employer desire to have Rooster Acquisition Corp., a Delaware
corporation, merge with and into REIT with REIT as the surviving corporation
(the "Merger"); and

         WHEREAS, as a result of the contemplated Merger, Employee and Employer
mutually agree that it is in the best interest of both parties for the timing of
the payment of the Change in Control Benefits under the Letter of Employment to
be amended and for the Employee to sign a waiver and release as a condition to
receiving the Change in Control Benefits under the Letter of Employment; and

         WHEREAS, Employee and Employer mutually agree that if the contemplated
Merger is either: (a) not effected or (b) not effected on or before April 30,
2002, this Amendment shall be without any force and effect and the timing of the
payment of the Change in Control Benefits and conditions for receiving the
Change in Control Benefits under the Letter of Employment shall at all times
commencing immediately after the execution of this Amendment be the timing of
payment of such benefits and conditions for receiving such benefits in effect
immediately prior to the execution of this Amendment.

         NOW, THEREFORE, for and in consideration of the mutual promises set
forth below, it is hereby agreed by and between the Employee and Employer as
follows:

         1.       The timing of the payment of the Change in Control Benefits
                  under the Letter of Employment shall be amended in its
                  entirety to provide as follows:

         The "lump sum payment" to be made pursuant to the terms of the Letter
of Employment shall be made no earlier than the thirtieth (30th) day and no
later than the forty-fifth (45th) day following the earliest to occur of:

         (a)      the effective time of the Merger;

         (b)      the termination of the Merger Agreement as a result of an
                  injunction  having  been  obtained against the Merger; or

         (c)      the 120th day following the close of the Tender Offer as
                  contemplated  and set forth in the Merger Agreement.

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         2.       As a condition to receiving the Change in Control Benefits
under this Letter of Employment, Employee must sign a waiver and release of all
claims arising out of Employee's termination and employment with Employer, in a
form reasonably satisfactory to Employer.

         3.       In the event the contemplated Merger is either: (a) not
effected or (b) not effected on or before April 30, 2002, this Amendment shall
be without any force and effect and the timing of the payment of the Change in
Control Benefits and conditions for receiving the Change in Control Benefits
under the Letter of Employment shall at all times commencing immediately after
the execution of this Amendment be the timing of payment of such benefits and
conditions for receiving such benefits in effect immediately prior to the
execution of this Amendment.

         4.       Employee, intending to be legally bound and for and in
consideration of the benefits described in this Amendment, does for himself, his
heirs, executors, administrators, successors and assigns, hereby release and
forever discharge Employer, its successors, predecessors, parents, subsidiaries,
affiliates, assigns, directors, officers, agents and employees and all persons,
corporations or other entities who might claim to be jointly and severally
liable with them, from any and all actions, causes of action, claims, demands,
charges or suits of any kind whatsoever based upon, arising out of or relating
to this Amendment.

         5.       Employee acknowledges that Employee has freely and voluntarily
entered into this Amendment and agrees that he shall not institute any legal
proceedings either individually or as a class representative or member against
Employer as to any matter based upon, arising out of or relating to this
Amendment.

         6.       This Amendment shall be governed by and construed in
accordance with the laws of the State of Massachusetts.

         7.       Except as provided herein, each provision of this Amendment is
intended to be severable. If any term or provision is held to be invalid, void
or unenforceable by a court of competent jurisdiction for any reason whatsoever,
such ruling shall not affect the remainder of this Amendment.

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         IN WITNESS WHEREOF, the parties, intending to be legally bound, apply
their signatures voluntarily and with full understanding of the contents of this
Amendment and after having had ample time to review and study this Amendment.

         Signed and executed this 5th day of December, 2001.

WITNESS:                                NEIL E. WAISNOR

                                        /s/ Neil E. Waisnor
                                        -------------------

WITNESS:                                CABOT INDUSTRIAL PROPERTIES, L.P.

                                        By: /s/ Ferdinand Colloredo-Mansfeld
                                            --------------------------------
                                        Title:  CEO

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