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                                                                   EXHIBIT 10.38

                       FOURTH AMENDMENT OF LEASE AGREEMENT


        THIS FOURTH AMENDMENT OF LEASE, made as of this 15th day of September,
1994, between REGIONAL INDUSTRIAL DEVELOPMENT CORPORATION OF SOUTHWESTERN
PENNSYLVANIA, a Pennsylvania nonprofit corporation having its principal office
in the City of Pittsburgh, Allegheny County, Pennsylvania (hereinafter called
the "Lessor"), and TOLLGRADE COMMUNICATIONS, INC., a Pennsylvania corporation
(hereinafter called the "Lessee").

        WHEREAS, the Lessor and Lessee previously made and entered into that
certain Lease Agreement, dated as of August 5, 1993, which was amended by the
First Amendment of Lease dated March 15, 1994, Second Amendment of Lease dated
July 1, 1994 and Third Amendment of Lease dated September 15, 1994 (hereinafter
collectively called the "Lease"), whereby Lessor leased to Lessee, upon terms
and conditions set forth therein, certain space (the "Premises") located in the
Harmar Industrial Manor (hereinafter called the "Complex") located in Harmar
Township, Allegheny County, Pennsylvania; and

        WHEREAS, the Lessor and the Lessee desire to amend the Lease upon the
terms and conditions set forth herein such that Lessee shall lease from Lessor
additional space in the Complex (hereinafter called the "Amendment of Lease").

        NOW THEREFORE, for good and valuable consideration, the receipt of which
hereby acknowledged, and intending to be legally bound hereby, Lessor and Lessee
covenant and agree as follows:

        1.      Incorporation by Reference/Capitalized Terms. The Lease is
hereby incorporated into this Amendment of Lease by reference



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and made an integral part hereof. Any capitalized term used in the Fourth
Amendment of Lease that is not otherwise defined herein shall have the
respective meaning ascribed to it in the Lease. In the event of a conflict
between the terms of this Amendment of Lease and the Lease, the terms of this
Amendment of Lease shall govern.

        2.      Premises. The Lessor does hereby lease and demise unto the
Lessee Units D-2, D-3 and D-5, containing approximately 4,440 rentable square
feet, in the Complex (hereinafter called the "Fifth Additional Space"). The
Fifth Additional Space is more particularly described on Exhibit "A", which is
attached hereto and made part hereof. The Fifth Additional Space shall be deemed
hereafter to be part of the Premises, as that term is defined in the Lease.

        3.      Commencement Date. The term of the Amendment of Lease shall
commence (hereinafter called the "Commencement Date") and possession shall be
given as of 12:01 AM on October 1, 1994. The Term of this Amendment of Lease
shall expire on the Expiration Date as set forth in the Lease unless the Term is
extended as provided in the Lease.

        4.      Base Rent. Lessee shall pay to Lessor at its office in
Pittsburgh, as monthly rental for the Fifth Additional Space, payable in advance
and without demand on the first business day of each successive calendar month
during the term of the lease, together with any escalations provided in the
Lease, following amount of ONE THOUSAND SIX HUNDRED SIXTY-FIVE AND 00/100
DOLLARS ($1665.00).

        If the Commencement Date is on a day other than the first



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business day of a calendar month, Lessee shall pay to Lessor on the date that
the first complete payment of Fifth Additional Space Base Rent is due, a pro
rata portion to be based on the number of days the Fifth Additional Space is
occupied in such partial month after the Commencement Date.

        5.      Full Force and Effect. Except as extended and amended hereby,
all other terms and conditions of the Lease shall remain unchanged and in full
force and effect and applicable to this Amendment of Lease.

        IN WITNESS WHEREOF, the parties hereto have caused this Fourth Amendment
of Lease to be executed the day and year first above written.

ATTEST:                                    REGIONAL INDUSTRIAL DEVELOPMENT
                                           CORPORATION OF SOUTHWESTERN
                                           PENNSYLVANIA

By /s/ Colleen B. Poremski                 By /s/ Frank Brooks Robinson
  ------------------------------             --------------------------
         Secretary                                 President

(Corporate Seal)



ATTEST:                                    TOLLGRADE COMMUNICATIONS, INC.


By /s/ Renee Sanders                       By /s/ Christian L. Allison
  ------------------------------             -------------------------
         V.P. Acct/Purchasing                      President



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                                    EXHIBIT A


[FLOOR PLAN OF FIFTH ADDITIONAL SPACE]