AMENDMENT OF RIGHTS AGREEMENT AND CERTIFICATION OF COMPLIANCE WITH SECTION 26

                                                                     Exhibit 4.3

                          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___________________________
                                             Name:
                                             Title:


Acknowledged and Agreed:
CONTINENTAL STOCK TRANSFER & TRUST COMPANY

By _____________________________
   Name:
   Title: