Exhibit 4 AMENDMENT OF RIGHTS AGREEMENT AND CERTIFICATION OF COMPLIANCE WITH SECTION 26

                                                                       Exhibit 4
                          AMENDMENT OF RIGHTS AGREEMENT
                                       AND
                   CERTIFICATION OF COMPLIANCE WITH SECTION 26

         Pursuant to Section 26 of the Rights Agreement ("Agreement") dated as
of June 28, 2001 between Mpower Holding Corporation (the "Company") and
Continental Stock Transfer & Trust Company (the "Rights Agent"), the Company and
the Rights Agent hereby amend the Agreement as of August 28, 2001 as provided
below.

         1. Paragraph 1(q) of the Agreement is hereby amended in full and
replaced in its entirety by the following:

                  "'Exempt Person' shall mean any of West Highland Partners,
         L.P., West Highland Capital, Inc., ▇▇. ▇▇▇▇ ▇. ▇▇▇▇▇▇▇, or Estero
         Partners, LLC (each an "Exempt Party"), provided that (i) during the
         period commencing on the date hereof and terminating at the close of
         business on December 15, 2001, the Exempt Parties collectively may
         acquire Beneficial Ownership of up to an additional 3,500,000 shares of
         Company Common Stock, (ii) in the event that after the close of
         business on December 15, 2001, an Exempt Party acquires Beneficial
         Ownership of any number of shares of Company Common Stock constituting
         more than 1% of the Company Common Stock then outstanding and such
         Exempt Party would otherwise be considered an Acquiring Person, such
         Exempt Party shall no longer be an Exempt Party and shall be an
         Acquiring Person and (iii) during the period between and inclusive of
         the dates set forth in clause (i), in the event that an Exempt Party
         acquires Beneficial Ownership of any number of shares of Company Common
         Stock in excess of the 3,500,000 shares referenced in clause (i), such
         Exempt Party shall no longer be an Exempt Party and shall be an
         Acquiring Person."

         The undersigned officer of the Company, being an appropriate officer of
the Company and authorized to do so by resolution of the board of directors of
the Company dated as of August 28, 2001, hereby certifies to the Rights Agent
that these amendments are in compliance with the terms of Section 26 of the
Agreement.

                                            MPOWER HOLDING CORPORATION


                                        By  /s/   ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                           -------------------------------------
                                           Name:  ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                           Title: Vice President and Secretary



Acknowledged and Agreed:

CONTINENTAL STOCK TRANSFER & TRUST COMPANY


By
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   Name:
   Title: