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                                                                 Exhibit 10.15.1

                                AMENDMENT NO. 1
                                      TO
                            STOCKHOLDERS' AGREEMENT

     This Amendment No. 1 (this "Amendment") is made as of October 13, 1999 to
the Stockholders' Agreement, dated as of September 9, 1999 (the "Stockholders'
Agreement"), by and among the undersigned parties thereto. All capitalized terms
used herein but not defined herein shall have the meanings given to them in the
Stockholders' Agreement.

                            PRELIMINARY STATEMENTS

     A.  Certain subsidiaries of the Corporation expect to establish a $10
million unsecured loan facility pursuant to a Loan Agreement (the "Loan
Agreement") with financial institutions named as "Lenders" therein (the
"Lenders") and Newcourt Commercial Finance Corporation, as administrative agent;

     B.  The Loan Agreement provides that, in connection with the transactions
contemplated thereby, the Corporation shall issue to the Lenders certain
warrants to purchase shares of its Class A Common Stock (the "Warrants"); and

     C.  The parties hereto desire to amend the Stockholders' Agreement to
exclude the Warrants, and the shares of Class A Common Stock issuable upon
exercise thereof, from the application of the preemptive rights contained in
Section 3 of the Stockholders' Agreement, and to amend certain other provisions
of the Stockholders' Agreement;

     NOW, THEREFORE, the undersigned parties agree as follows:

     1.  Section 2.1 of the Stockholders' Agreement is hereby amended to
insert the following at the end of the last sentence of such Section:

         "plus the total number of Securities that holders thereof have the
         right to Transfer in such transaction as a result of any other tag-
         along, co-sale or similar rights granted in accordance with Section 2.6
         hereof."

     2.  Section 3.1 of the Stockholders' Agreement is hereby amended to
insert a sentence at the end of such Section, to read in its entirety as
follows:

         "Furthermore, the provisions of this Section 3.1 shall not apply to the
         issuance of any warrants (or any Securities issuable upon exercise of
         such
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         warrants) in connection with the $10 million unsecured loan facility
         established under a Loan Agreement, by and among certain wholly-owned
         subsidiaries of the Corporation, financial institutions named as
         "Lenders" therein and Newcourt Commercial Finance Corporation, as
         administrative agent.

     3.  Schedule 3.1 of the Stockholders' Agreement is hereby amended to
replace the number "1,967,437" appearing thereon with "2,401,258".

     IN WITNESS WHEREOF, the parties have executed and delivered this Amendment
as of the date first written above.

                              THE CORPORATION:

                              PAETEC CORP.

                              By:/s/ Arunas A. Chesonis
                                 -----------------------------
                              Name: Arunas A. Chesonis
                              Title: President and Chief Executive Officer

                              MAJORITY STOCKHOLDERS:

                               /s/ Arunas A. Chesonis
                              -----------------------------
                              Arunas A. Chesonis


                              CHRISTOPHER E. EDGECOMB
                              LIVING TRUST, dated April 25, 1998

                              /s/ Christopher Edgecomb
                              -----------------------------
                              Christopher Edgecomb, Trustee


                              /s/ Jeffrey Sudikoff
                              -----------------------------
                              Jeffrey Sudikoff
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                              CCS GROUP STOCKHOLDERS:

                              ALLIANCE CABLETEL HOLDINGS, L.P., a
                              Delaware limited partnership

                              By: KOCOM COMMUNICATIONS, INC., a
                              Delaware limited partnership


                              By: /s/ James A. Kofalt
                                 -------------------------------
                                  James A. Kofalt, President


                              KLINE HAWKES CALIFORNIA SBIC, L.P.


                              By: [Signature Illegible]
                                 -------------------------------
                                   Its: Chairman


                              THE UNION LABOR LIFE INSURANCE
                              COMPANY SEPARATE ACCOUNT P


                              By: [Signature Illegible]
                                 -------------------------------
                                  Its: VP Investments



                              /s/ Robert I. Schwartz
                              -----------------------------
                              Robert I. Schwartz


                              /s/ Kenneth M. Kiraly
                              -----------------------------
                              Kenneth M. Kiraly


                              /s/ Susan F. Kiraly
                              -----------------------------
                              Susan F. Kiraly

                                       3
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                              /s/ Richard P. Rizzutti
                              ------------------------------------
                              Richard P. Rizzutti


                              /s/ Bryant Hopper
                              -------------------------------------
                              Bryant Hopper


                              /s/ Ronald S. Johnson
                              -------------------------------------
                              Ronald S. Johnson


                              /s/ Lodwrick Cook
                              -------------------------------------
                              Lodwrick Cook


                              /s/ Peter Cracovaner
                              -------------------------------------
                              Peter Cracovaner


                              /s/ Richard Cunningham
                              -------------------------------------
                              Richard Cunningham


                              /s/ Thomas O. FitzGerald
                              -------------------------------------
                              Thomas O. FitzGerald


                              /s/ Wendy Foliano
                              -------------------------------------
                              Wendy Foliano


                              /s/ Joseph Golden
                              -------------------------------------
                              Joseph Golden


                              /s/ Stephen Mayo
                              -------------------------------------
                              Stephen Mayo

                                       4
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                              /s/ Karen Sancimino
                              --------------------------------
                              Karen Sancimino


                              /s/ Clinton Walker
                              --------------------------------
                              Clinton Walker

                                       5