<PAGE>
                                                                   Exhibit 10.8

                      FOURTH AMENDMENT TO CREDIT AGREEMENT


         THIS FOURTH AMENDMENT TO CREDIT AGREEMENT, dated as of June 20, 2003
(this "Amendment"), is by and among BLACK BOX CORPORATION OF PENNSYLVANIA, a
Delaware corporation (the "Borrower"), BLACK BOX CORPORATION, a Delaware
corporation (the "Parent"), the other guarantors to the Credit Agreement
(together with the Parent, the "Guarantors"), the lenders parties to the Credit
Agreement (the "Lenders") and CITIZENS BANK OF PENNSYLVANIA, a national banking
association, as agent for the Lenders (in such capacity, the "Agent") and as
Swingline Lender.

                              W I T N E S S E T H:

         WHEREAS, the Borrower, the Guarantors, the Lenders and the Agent are
parties to a Credit Agreement, dated as of April 4, 2000, and amended by that
certain First Amendment to Credit Agreements, dated as of March 30, 2001, that
certain Second Amendment to Credit Agreements, dated as of April 3, 2002 and
that certain Third Amendment to Credit Agreement, dated as of the date hereof
(as so amended, the "Credit Agreement"), pursuant to which the Lenders have
agreed, on the terms and subject to the conditions described therein, to make
Loans to the Borrower; and

         WHEREAS, the commitments of the Lenders under the Short Term Credit
Agreement, dated as of April 4, 2000, as amended, among the Borrower, the
Guarantors, the Lenders and the Agent have been terminated; and

         WHEREAS, the Borrower has requested the Lenders and the Agent to make
certain changes to the Credit Agreement, including, without limitation, the
establishment of a Swingline facility under the Credit Agreement; and

         WHEREAS, the Lenders and the Agent are willing to amend the Credit
Agreement as set forth below; and

         WHEREAS, capitalized terms used herein and not otherwise defined shall
have the meanings assigned to them in the Credit Agreement;

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants herein contained, and intending to be legally bound hereby, the
parties hereto agree as follows:

         SECTION 1. Amendments to Credit Agreement with respect to Issuing
Banks. The Credit Agreement is hereby amended as follows:

         1.1. The respective definitions of the terms "Issuing Banks" and
"Issuing Bank Representative" appearing in Section 1.01 of the Credit Agreement
are hereby amended to read in its entirety as follows:

                  "Issuing Banks" shall mean (i) with respect to Letters of
         Credit issued prior to June , 2003, Mellon Bank, N. A. and such of its
         affiliates as Mellon Bank, N. A. may (subject to the approval of the
         Borrower, such approval not to be unreasonably withheld) from time to
         time elect to cause to issue Letters of Credit and (ii) with respect to
         Letters of Credit issued or to be issued from and after June , 2003,
         Citizens Bank of Pennsylvania


<PAGE>

         and such of its affiliates as Citizens Bank of Pennsylvania may
         (subject to the approval of the Borrower, such approval not to be
         unreasonably withheld) from time to time elect to cause to issue any
         one or more of such Letters of Credit. "Issuing Bank" shall mean, with
         respect to a Letter of Credit, the issuer of such Letter of Credit and
         references to "the Issuing Bank" and similar references shall be deemed
         to mean "each Issuing Bank with respect to Letters of Credit issued or
         to be issued by it".

                  "Issuing Bank Representative" shall mean (i) with respect to
         Letters of Credit issued prior to June 20, 2003, Mellon Bank, N. A. and
         (ii) with respect to Letters of Credit issued or to be issued from and
         after June 20, 2003, Citizens Bank of Pennsylvania.

         SECTION 2. Amendments to Credit Agreement with respect to Swingline
Loans. The Credit Agreement is hereby amended as follows:

         2.1. Section 1.01 of the Credit Agreement is hereby amended by adding
thereto, in appropriate alphabetical sequence, the following definitions:

                  "Applicable Swingline Margin" has the meaning ascribed thereto
         in Section 2.14.

                  "London Business Day" has the meaning ascribed thereto in
         Section 2.14.

                  "Swingline Interest Period", "Swingline Interest Payment Date"
         and "Swingline LIBOR Rate" have the respective meaning ascribed thereto
         in Section 2.14.

                  "Swingline Lender" shall mean Citizens Bank of Pennsylvania.

                  "Swingline Loans" has the meaning ascribed thereto in Section
         2.13.

                  "Swingline Note" shall mean a promissory note of the Borrower,
         in the form of Annex B to the Fourth Amendment to this Agreement,
         appropriately completed.

         2.2. The respective definition of the terms "Lender", "Loan",
"Revolving Credit Exposure" and "Revolving Credit Extensions of Credit"
appearing in Section 1.01 of the Credit Agreement is hereby amended are read as
follows:

                  "Lender" shall mean any of the Lenders listed on the signature
         pages hereof, subject to the provions of Section 10.14 hereof
         pertaining to Persons becoming or ceasing to be Lenders. "Lender" shall
         in any event include the Issuing Banks and the Swingline Lender.

                  "Loan" shall mean any loan by a Lender to the Borrower under
         this Agreement, including without limitation any Swingline Loan, and
         "Loans" shall mean all loans made by the Lenders under this Agreement.

                  "Revolving Credit Exposure" of any Lender at any time shall
         mean the sum at such time of the outstanding principal amount of such
         Lender's Revolving Credit Loans plus such Lender's Pro Rata share of
         the sum of the aggregate Letter of Credit Exposure plus such Lender's
         Pro Rata share of the outstanding principal amount of Swingline Loans.



<PAGE>

                  "Revolving Credit Extensions of Credit" shall mean, at any
         particular time, the sum of (a) the aggregate unpaid principal amount
         of Revolving Credit Loans then outstanding, (b) the aggregate Letter of
         Credit Obligations then outstanding and (c) the aggregate unpaid
         principal amount of Swingline Loans then outstanding; provided,
         however, that for purposes of determining the amount of Commitment Fee
         payable to each Lender under Section 2.02, the amount of Swingline
         Loans outstanding shall be attributable only to the Swingline Lender
         and not to any other Lender, except to the extent a Lender has funded
         its participation interest in a Swingline Loan, in which case the
         amount of such funding shall be attributable to such Lender and not to
         the Swingline Lender.

         2.3 The Credit Agreement is hereby amended by adding thereto, in
appropriate numerical sequence, new Sections 2.13 and 2.14 as set out on Annex A
hereto.

         2.4 Section 8.02(a)(i) of the Credit Agreement is hereby amended by
deleting the phrase "Declare the Revolving Credit Commitment terminated,
whereupon the Commitments will terminate" appearing therein and inserting in
lieu thereof the phrase "Declare the Revolving Credit Commitment and the
commitment of the Swingline Lender to make Swingline Loans terminated, whereupon
the Commitments and such commitment to make Swingline Loans will terminate".

         2.5 Section 8.02(b) of the Credit Agreement is hereby amended by
deleting the phrase "the Commitments shall automatically terminate" appearing
therein and inserting in lieu thereof the phrase "the Commitments and the
commitment of the Swingline Lender to make Swingline Loans shall automatically
terminate".

         2.6. Section 10.03 of the Credit Agreement is hereby amended by
redesignating paragraph (g) thereof as paragraph (h) and by adding thereto, in
appropriate sequence, a new paragraph (g) to read as follows:

                  (g) Amend or waive any of the provisions of Section 2.13 or
         2.14 hereof, or impose additional duties upon the Swingline Lender or
         otherwise adversely affect the rights, interests or obligations of the
         Swingline Lender, without the written consent of the Swingline Lender;
         or

         SECTION 3.  Miscellaneous.

         3.1. Effect of Amendment. This Amendment shall become effective upon
(a) the execution by the Borrower, the Guarantors, the Lenders and the Agent,
and delivery to the Agent, of this Amendment, (b) the execution by the Borrower
and delivery to the Swingline Lender of the Swingline Note, dated the date of
this Amendment, in the form attached hereto as Annex B, (c) receipt by the Agent
of an opinion in form and substance satisfactory to the Agent from counsel to
each of the Loan Parties as to such matters relating to this Amendment, the
Swingline Loans and the Swingline Notes as the Agent may request, and (d)
receipt by the Agent of such other certificates, corporate documents and other
documents as the Agent may request. The Credit Agreement, as amended by this
Amendment, is in all respects ratified, approved and confirmed and shall, as so
amended, remain in full force and effect.

         3.2. Confirmation of Guaranty. Each of the Guarantors reaffirms the
terms and conditions of the Loan Documents executed by it and acknowledges and
agrees that such Loan Documents remain in full force and effect and are hereby
ratified, reaffirmed and confirmed.


<PAGE>

Without limiting the generality of the foregoing, each of the Guarantors
confirms and agrees that the Swingline Loans and the Swingline Notes are
"Guaranteed Obligations" under the Credit Agreement and the other Loan
Documents, including without limitation the Guaranty and Suretyship Agreement to
which such Guarantor is a party.

         3.3. Governing Law. This Amendment shall be governed by and construed
in accordance with the laws of the Commonwealth of Pennsylvania without giving
effect to the conflict of law principles thereof.

         3.4. Counterparts. This Amendment may be executed in any number of
counterparts and by the different parties hereto on separate counterparts, each
of which, when so executed, shall be deemed an original, but all such
counterparts shall constitute but one and the same instrument.


                         [SIGNATURES BEGIN ON NEXT PAGE]



<PAGE>



         SIGNATURE PAGE 1 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



         IN WITNESS WHEREOF, the parties hereto, by their officers thereunto
duly authorized, have executed and delivered this Amendment as of the date first
above written.


                                       BORROWER:

                                       BLACK BOX CORPORATION OF PENNSYLVANIA

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



                                       GUARANTORS:

                                       BLACK BOX CORPORATION and each of the
                                       DOMESTIC SUBSIDIARIES listed on Annex C
                                       attached hereto and made a part hereof

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------
                                              of Black Box Corporation and of
                                              each of the Domestic Subsidiaries
                                              listed on Annex C hereto





<PAGE>



         SIGNATURE PAGE 2 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.

                                       AGENT:

                                       CITIZENS BANK OF PENNSYLVANIA

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



                                       BANKS:

                                       CITIZENS BANK OF PENNSYLVANIA

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------





<PAGE>



         SIGNATURE PAGE 3 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                        WITH BLACK BOX CORPORATION ET AL.



                                       WACHOVIA BANK, NATIONAL ASSOCIATION

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------


<PAGE>



         SIGNATURE PAGE 4 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       FLEET NATIONAL BANK

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------





<PAGE>



         SIGNATURE PAGE 5 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       NATIONAL CITY BANK OF PENNSYLVANIA

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



<PAGE>



         SIGNATURE PAGE 6 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       COMERICA BANK

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



<PAGE>



         SIGNATURE PAGE 7 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       FIRSTAR BANK, N.A.

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



<PAGE>



         SIGNATURE PAGE 8 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       KEYBANK NATIONAL ASSOCIATION

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



<PAGE>



         SIGNATURE PAGE 9 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       MELLON BANK, N. A.

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------



<PAGE>



         SIGNATURE PAGE 10 OF 10 TO FOURTH AMENDMENT TO CREDIT AGREEMENT
                       WITH BLACK BOX CORPORATION ET AL.



                                       FIFTH THIRD BANK

                                       By:
                                           ------------------------------------

                                       Name:
                                             ----------------------------------

                                       Title:
                                              ---------------------------------




<PAGE>



                 ANNEX A TO FOURTH AMENDMENT TO CREDIT AGREEMENT


         2.13. SWINGLINE LOANS.

         (a) The Swing Line. Subject to the terms and conditions set forth
herein (including without limitation the conditions set forth in Section 5.02
hereof), the Swingline Lender agrees to make loans (each such loan, a "Swingline
Loan") in Dollars, to the Borrower from time to time on any Business Day during
the period from the Closing Date to the Revolving Credit Maturity Date in an
aggregate amount not to exceed Five Million Dollars outstanding at any time;
provided, however, that after giving effect to any Swingline Loan, (i) the
aggregate outstanding amount of all Revolving Credit Loans, Swingline Loans and
Letter of Credit Obligations shall not exceed the Aggregate Revolving Credit
Committed Amounts of all Lenders and (ii) the aggregate outstanding amount of
the Revolving Credit Loans of any Lender other than the Swingline Lender, plus
such Revolving Lender's Pro Rata share of the outstanding amount of all Letter
of Credit Obligations, plus such Lender's Pro Rata share of the outstanding
amount of all Swingline Loans shall not exceed such Lender's Revolving Credit
Committed Amount. Within the foregoing limits, and subject to the other terms
and conditions hereof, the Borrower may borrow, prepay and reborrow under this
Section 2.13. To the extent not due and payable earlier, the Swingline Loans
shall be due and payable on the Revolving Credit Maturity Date. Each Swingline
Loan shall bear interest as set forth in Section 2.14. Immediately upon the
making of a Swingline Loan, each Lender shall be deemed to, and hereby
irrevocably and unconditionally agrees to, purchase from the Swingline Lender a
risk participation in such Swingline Loan in an amount equal to the product of
such Revolving Lender's Pro Rata share times the amount of such Swingline Loan.
The Swingline Loans shall be evidenced by the Swingline Note.

         (b) Borrowing Procedures. If the Borrower desires that the Swingline
Lender make a Swingline Loan, the Borrower shall give irrevocable notice to the
Swingline Lender, which may be given by telephone. Each such notice must be
received by the Swingline Lender not later than 12:00 noon, Pittsburgh time on
the requested borrowing date, and shall specify (i) the amount to be borrowed,
which may be any amount, and (ii) the requested borrowing date, which shall be a
Business Day. Each such telephonic notice shall be confirmed promptly by
delivery to the Swingline Lender and the Administrative Agent of a written
confirmation thereof. After receipt by the Swingline Lender of request of a
Swingline Loan, the Swingline Lender shall make the proceeds of such Swingline
Loan available to the Borrower on the borrowing date specified in such notice
available to the Borrower at the Swingline Lender's office by crediting the
account of the Borrower on the books of the Swingline Lender in funds
immediately available at such office.

         (c) Refinancing of Swingline Loans.

                  (i) The Swingline Lender at any time in its sole and absolute
         discretion may request, on behalf of the Borrower (which hereby
         irrevocably authorizes the Swingline Lender to so request on its
         behalf), and the Borrower at any time may request, that a Revolving
         Loan be made in an amount equal to the amount of some or all of the
         Swingline


<PAGE>

         Loans then outstanding. Such request shall be made in accordance with
         the requirements of Section 2.03, without regard to the minimum and
         multiples specified therein for the principal amount of Revolving
         Credit Loans, but subject to the unutilized portion of the Aggregate
         Revolving Credit Committed Amounts and to satisfaction of the
         conditions set forth in Section 5.02. Each Lender shall make an amount
         equal to its Pro Rata share of the amount specified in the applicable
         Standard Notice available to the Agent in funds immediately available
         at the Agent's Office for the account of the Swingline Lender not later
         than 2:00 p.m., Pittsburgh time, on the Business Day specified in such
         notice, whereupon, subject to Section 2.13(c)(ii), each Lender that so
         makes funds available shall be deemed to have made a Revolving Loan
         bearing interest at the Base Rate Option to the Borrower in such
         amount. The Administrative Agent shall remit the funds so received from
         the Lenders to the Swingline Lender.

                  (ii) If for any reason the making of Revolving Loans cannot be
         requested in accordance with Section 2.13(c)(i) or any Swingline Loan
         cannot be refinanced by the making of Revolving Loans, the Standard
         Notice submitted by the Swingline Lender as contemplated by Section
         2.13(c)(i) shall be deemed to be a request by the Swingline Lender that
         each of the Lenders fund its risk participation in the amount of the
         relevant Swingline Loan and each Revolving Lender's payment to the
         Administrative Agent for the account of the Swingline Lender pursuant
         to Section 2.05(c)(i) shall be deemed payment in respect of such risk
         participation in the amount of such Swingline Loan.

                  (iii) If any Lender fails to make available to the Agent for
         the account of the Swingline Lender any amount required to be paid by
         such Lender pursuant to the foregoing provisions of this Section
         2.13(c) by the time specified in Section 2.13(c)(i), the Swingline
         Lender shall be entitled to recover from such Lender, on demand, such
         amount with interest thereon for the period from the date such payment
         is required to the date on which such payment is immediately available
         to the Swingline Lender at a rate per annum equal to the applicable
         Federal Funds Rate for three Business Days and thereafter at a rate per
         annum equal to the rate applicable to the relevant Swingline Loan. A
         certificate of the Swingline Lender submitted to any Lender with
         respect to any amounts owing under this clause (iii) shall be
         conclusive absent manifest error.

                  (iv) Each Lender's obligation to make Revolving Credit Loans
         or to purchase and fund risk participations in Swingline Loans pursuant
         to this Section 2.13(c) shall be absolute and unconditional and shall
         not be affected by any circumstance, including (A) any set-off,
         counterclaim, recoupment, defense or other right which such Lender may
         have against the Swingline Lender, the Borrower or any other Person for
         any reason whatsoever, (B) the occurrence or continuance of a Potential
         Default or Event of Default, or (C) any other occurrence, event or
         condition, whether or not similar to any of the foregoing; provided,
         however, that each Lender's obligation to make Revolving Loans pursuant
         to this Section 2.13(c) is subject to the conditions set forth in
         Section 5.02. Any such purchase of risk participations by each Lender
         from the Swingline Lender shall not relieve or otherwise


<PAGE>

         impair the obligation of the Borrower to repay Swingline Loans,
         together with interest as provided herein.

         (d) Repayment of Participations.

                  (i) At any time after any Lender has purchased and funded a
         risk participation in a Swingline Loan, if the applicable Swingline
         Lender receives any payment on account of such Swingline Loan, such
         Swingline Lender will distribute to such Lender its ratable share of
         such payment (appropriately adjusted, in the case of interest payments,
         to reflect the period of time during which such Revolving Lender's risk
         participation was outstanding and funded).

                  (ii) If any payment received by the Swingline Lender in
         respect of principal or interest on any Swingline Loan is required to
         be returned by the Swingline Lender, each Lender shall pay to the
         Swingline Lender its Pro Rata share of such amount on demand of the
         Swingline Lender, plus interest thereon from the date of such demand to
         the date such amount is returned at a rate per annum equal to the
         applicable Federal Funds Rate.

         (e) Interest for Account of Swingline Lender. The Swingline Lender
shall be responsible for invoicing the Borrower for interest on the Swingline
Loans. Until each Lender funds its Revolving Credit Loan or risk participation
pursuant to this Section 2.05, interest in respect of such Lender's Pro Rata
share of the applicable Swingline Loans shall be solely for the account of the
Swingline Lender.

         2.14. INTEREST ON AND PAYMENT OF SWINGLINE LOANS; OTHER MATTERS.

         (a) Certain Definitions. As used herein, the following terms have the
following meanings:

                  (i) "Applicable Swingline Margin" for any day means
         one-quarter of one percent (0.25%) in excess of the Applicable Margin
         (as defined in Section 2.04(b) hereof) for such day.

                  (ii) "Swingline Interest Period" means, initially, the period
         commencing on June [30], 2003 (the "Start Date") and ending on the
         numerically corresponding date one month later, and thereafter each one
         month period ending on the day of such month that numerically
         corresponds to the Start Date. If a Swingline Interest Period is to end
         in a month for which there is no day which numerically corresponds to
         the Start Date, the Interest Period will end on the last day of such
         month.

                  (iii) "Swingline Interest Payment Date" means, initially, July
         [30], 2003, and thereafter the numerically corresponding date of each
         month. If a month does not contain a day that numerically corresponds
         to the initial Interest Payment Date, the Interest Payment Date shall
         be the last day of such month.

                  (iv) "Swingline LIBOR Rate" means, relative to any Swingline
         Interest Period, the offered rate for delivery in two London Banking
         Days (as defined below) of deposits of


<PAGE>

         U.S. Dollars which the British Bankers' Association fixes as its LIBOR
         rate and which appears on the Telerate Page 3750 as of 11:00 a.m.
         London time on the day on which such Swingline Interest Period
         commences, and for a period approximately equal to such Interest
         Period. If the first day of any Swingline Interest Period is not a day
         which is both a (x) Business Day and (y) a day on which U.S. Dollar
         deposits are transacted in the London interbank market (a "London
         Business Day"), the Swingline LIBOR Rate shall be determined in
         reference to the next preceding day which is both a Business Day and a
         London Banking Day. If for any reason the Swingline LIBOR Rate is
         unavailable and/or the Swingline Lender is unable to determine the
         Swingline LIBOR Rate for any Swingline Interest Period, the Swingline
         LIBOR Rate shall be deemed to be equal to the Base Rate.

         (b) Interest Rates for Swingline Loans. Except as otherwise provided in
this Section 2.14, the Swingline Loans shall bear interest for each day at a
rate per annum equal to the sum of Swingline LIBOR Rate for the Swingline
Interest Period during which such day occurs plus the Applicable Swingline
Margin for such day; provided, however, that if the Swingline LIBOR rate is
equal to the Base Rate as contemplated by the last sentence of Section 2.14(a),
the Applicable Swingline Margin shall be deemed to be zero. Interest on
Swingline Loans shall be payable on each Swingline Interest Payment Date. For
avoidance of doubt, Section 2.09(c)(ii) shall apply to Swingline Loans.
Notwithstanding anything to the contrary in this Agreement, if participations of
the Lenders in any Swingline are funded as contemplated by Section 2.13(c), such
Swingline Loan shall, as of the date the request for such funding is made by the
Swingline Lender, bear interest at the Base Rate Option as provided in Section
2.04 rather than at the rate set forth in the first sentence of this Section
2.14(b).

         (c) Payments and Prepayments of Swingline Loans. The Borrower shall
have the right at any time to prepay Swingline Loans without premium or penalty
by giving notice to the Swingline Lender and the Agent of such intended
prepayment not later than 11:00 a.m. Pittsburgh time on the date of such
proposed prepayment. Section 2.09(b) hereof shall apply to payments of Swingline
Loans. In addition, the Borrower and the Swingline Lender may from time to time
agree to arrangements whereby Swingline Loans are repaid by a "sweep" or similar
mechanism.

         (d) Other Matters with respect to Swingline Loans. References in
Article IX of this Agreement to the Issuing Bank shall be deemed to be
references to each of the Issuing Bank and the Swingline Lender.



<PAGE>



                           ANNEX B TO FOURTH AMENDMENT

                             FORM OF SWINGLINE NOTE



                                 Swingline Note



$5,000,000                                             Pittsburgh, Pennsylvania
                                                                   June  , 2003


         FOR VALUE RECEIVED, the undersigned, BLACK BOX CORPORATION OF
PENNSYLVANIA, a Delaware corporation (the "Borrower"), promises to pay to the
order of CITIZENS BANK OF PENNSYLVANIA (the "Lender") on or before the Revolving
Credit Maturity Date (as defined in the Agreement referred to below), and at
such earlier dates as may be required by such Agreement, the lesser of (i) the
principal sum of Five Million Dollars ($5,000,000) or (ii) the aggregate unpaid
principal amount of all Swingline Loans made by the Lender to the Borrower from
time to time pursuant to the Agreement. The Borrower further promises to pay to
the order of the Lender interest on the unpaid principal amount hereof from time
to time outstanding at the rate or rates per annum determined pursuant to
Section 2.14 of, or as otherwise provided in, the Agreement, payable on the
dates set forth in Section 2.14 of, or as otherwise provided in, the Agreement.

         All payments of principal and interest hereunder shall be due and
payable by 12:00 Noon, Pittsburgh time, on the day when due. Such payments shall
be made to the Agent, for the benefit of the Lender, at its Office in Dollars in
immediately available funds without setoff, counterclaim or other deduction of
any nature.

         Except as otherwise provided in the Agreement, if any payment of
principal or interest hereunder shall become due on a day which is not a
Business Day, such payment shall be made on the next following Business Day and
such extension of time shall be included in computing interest in connection
with such payment.

         This Note is the "Swingline Note" as referred to in, and is entitled to
the benefits of the Credit Agreement, dated as of April 4, 2000, as amended, by
and among the Borrower, the Lenders party thereto from time to time, the
Guarantors party thereto from time to time, and Citizens Bank of Pennsylvania,
as Agent (as the same may be further amended, modified or supplemented from time
to time, the "Agreement"), which among other things provides for the
acceleration of the maturity hereof upon the occurrence of certain events and
for prepayments in certain circumstances and upon certain terms and conditions.
Terms defined in the Agreement have the same meanings herein.


<PAGE>

         The Borrower hereby expressly waives presentment, demand, notice,
protest and all other demands and notices in connection with the delivery,
acceptance, performance, default or enforcement of this Note and the Agreement,
and an action for amounts due hereunder or thereunder shall immediately accrue.

         This Note shall be governed by, construed and enforced in accordance
with the laws of the Commonwealth of Pennsylvania, without regard to principles
of conflicts of law.

                                          BLACK BOX CORPORATION OF PENNSYLVANIA


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






<PAGE>



                           ANNEX C TO FOURTH AMENDMENT

                       GUARANTORS - DOMESTIC SUBSIDIARIES



BBox Holding Company
Atimco Network Services, Inc.
American Telephone Wiring Company
Midwest Communications Technologies, Inc.
Associated Network Solutions, Inc.
Advanced Communications Corporation
Cable Consultants, Incorporated
Todd Communications, Inc.
Comm Line, Inc.
Business Communications Concepts, Inc.
Koncepts Communications of L.I., Corp.
Communication Contractors, Inc.
DataCom-Link, Inc.
U.S. Premise Networking Services, Inc.
TennMark Telecommunications, Inc.
Parrish Communications Cabling, Inc.
R&D Services, Inc.
Delaney Telecom, Inc.
Delaney Electrical Services, Inc.
K&A Communications, Inc.
Jet Line Communications, Inc.
A.T.S., Inc.
Coast to Coast Communications, Inc.
Advanced Network Technologies, Inc.
BB Technologies, Inc.