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                                                                   EXHIBIT 10.35


                       FIRST AMENDMENT OF LEASE AGREEMENT


        THIS FIRST AMENDMENT OF LEASE AGREEMENT, made this 15th day of March
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 (hereinafter called the
"Lease"), whereby Lessor leased to Lessee, upon the terms and conditions set
forth therein, certain office 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 Lessee desire to amend the Lease upon the terms
and conditions as set forth herein such that Lessee shall lease from Lessor
additional office space in the Complex (hereinafter called the "Amendment to
Lease").

        NOW THEREFORE, for good and valuable consideration, the receipt of which
is 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 and made an
integral part hereof. Any capitalized term used in the 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 Suite 105 containing approximately Two Thousand One Hundred Fifty Four
square feet (2,154 sq. ft.) of rentable area of existing office space in the
Complex (hereinafter called "First Additional Space"). The First Additional
Space is more particularly described on EXHIBIT A, which is attached hereto and
made part hereof. The First 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 this Amendment of Lease shall
commence (hereinafter called the "Commencement Date") and possession shall be
given as of 12:01 AM on March 15, 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.



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        4.      Base /Rent. Lessee shall pay to Lessor at its office in
Pittsburgh, the sum of One Thousand Three Hundred and Forty Six Dollars
($1,346.00) as monthly rental for the First Additional Space, payable in advance
and without demand on or before the first business day of each successive
calendar month for the duration of the Term of the Lease, and any renewal
thereof (hereinafter called "First Additional Space Base Rent").

        If the Commencement Date is on a day other than the first business day
of a calendar month, Lessee shall pay to Lessor on the date that the first
complete payment of First Additional Space Base Rent is due, a pro rata portion
to be based on the number of days the First 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.



                                      -2-
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        IN WITNESS WHEREOF, the parties hereto have caused this Amendment of
Lease to be duly executed the day and year first above written.


ATTEST                                     REGIONAL INDUSTRIAL DEVELOPMENT
                                           CORPORATION OF SOUTHWESTERN
                                           PENNSYLVANIA



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




ATTEST:                                    TOLLGRADE COMMUNICATIONS, INC'


/s/ Carole A. Mitchell                     By:  /s/ Christian L. Allison
--------------------------------                -------------------------------
                                           Name:  CHRISTIAN L. ALLISON
                                                -------------------------------
                                           Title:  PRESIDENT
                                                 ------------------------------



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                                    EXHIBIT A


[FLOOR PLAN OF FIRST ADDITIONAL SPACE]