Exhibit 99.1




                            Amendment No. 1 to the
                               Rights Agreement
                            of Eastern Enterprises

         This  Amendment  No. 1, dated as of April 26,  2000,  amends the Rights
Agreement  dated as of July 22, 1998 (the "Rights  Agreement"),  between Eastern
Enterprises,  a Massachusetts  business trust (the "Trust"),  and Fleet National
Bank (formerly known as BankBoston, N.A.), as Rights Agent (the "Rights Agent").
Terms defined in the Rights Agreement and not otherwise  defined herein are used
herein as so defined.

                             W I T N E S S E T H:
                            --------------------

         WHEREAS, on July 22, 1998 the Board of Trustees of the Trust authorized
the issuance of Rights to purchase,  on the terms and subject to the  provisions
of the Rights Agreement, shares of the Trust's Common Stock;

         WHEREAS,  on  July  22,  1998,  the  Board  of  Trustees  of the  Trust
authorized and declared a dividend  distribution of one Right for every share of
Common Stock of the Trust outstanding on the Dividend Record Date and authorized
the  issuance of one Right  (subject to certain  adjustments)  for each share of
Common  Stock of the Trust  issued  between  the  Dividend  Record  Date and the
Distribution Date;

         WHEREAS, the Distribution Date has not occurred; and

         WHEREAS,  pursuant to Section 27 of the Rights Agreement, the Board has
approved an amendment of certain provisions of the Rights Agreement as set forth
below;

         NOW, THEREFORE, the Rights Agreement is hereby amended as follows:

         1.       Section 1(b) is amended by deleting the phrase "or (v)"
after clause (iv) and adding the following language:

         ", (v) an Exempt Person, or (vi)".

         2.       A new definition is added after Section 1(u) and before
Section 1(v) as follows:





         "(u*)  "Exempt  Person"  shall  mean  KeySpan  Corporation,  a New York
corporation,  and its subsidiaries  solely to the extent any such Person becomes
the  Beneficial  Owner  of 10% or  more  of the  shares  of  Common  Stock  then
outstanding by reason of the  consummation of the  transactions  contemplated by
the Agreement and Plan of Merger,  dated as of November 4, 1999, as amended (the
"Merger  Agreement"),  by and  among  the  Trust,  KeySpan  Corporation  and ACJ
Acquisition LLC; provided,  that this Section 1(u*) shall be of no further force
and effect at and after such time as the Merger Agreement is terminated pursuant
to Section 9.01 thereof.

         3.       Section 24(a) is amended by deleting the phrase "or (iv)"
after clause (iii) in the last sentence and adding the following language:

         ", (iv) an Exempt Person, or (v)".

         4.  Governing  Law.  This  Amendment to the Rights  Agreement  shall be
deemed to be a contract made under the laws of The Commonwealth of Massachusetts
and for all purposes  shall be governed by and construed in accordance  with the
laws of said  Commonwealth  applicable  to  contracts  to be made and  performed
entirely within said Commonwealth.

         5.       Counterparts.  This Amendment to the Rights Agreement may be
executed in any number of counterparts and each of such counterparts shall for
all purposes be deemed to be an original, and all such counterparts shall
together constitute but one and the same instrument.

         6.  Amendment;  Ratification of Rights  Agreement.  Except as expressly
noted herein, this Amendment to the Rights Agreement shall not by implication or
otherwise  alter,  modify,  amend  or in  any  way  affect  any  of  the  terms,
conditions,  obligations,  covenants  or  agreements  contained  in  the  Rights
Agreement,  all of which are  ratified  and  affirmed in all  respects and shall
continue in full force and effect.

         7.  Severability.  If any term,  provision,  covenant or restriction of
this  Amendment  to the  Rights  Agreement  is  held  by a  court  of  competent
jurisdiction  or other  authority  to be  invalid,  void or  unenforceable,  the
remainder of the terms, provisions, covenants and restrictions of this Amendment
to the Rights Agreement, and of the Rights Agreement, shall remain in full force
and effect and shall in no way be affected, impaired or invalidated.

         8. The Trust.  Reference  is hereby  made to the  declaration  of trust
establishing  the Trust dated July 18, 1929,  as amended,  a copy of which is on
file  in  the  office  of  the  Secretary  of  State  of  The   Commonwealth  of
Massachusetts.  The name "Eastern Enterprises" refers to the trustees under such
declaration as trustees and not personally. No trustee, shareholder,  officer or
agent of the Trust shall be held to any personal  liability in  connection  with
the affairs of the Trust and only the trust estate may be liable.


                                ********





         IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1
to the Rights  Agreement to be duly  executed as of the day and year first above
written.

                                                     EASTERN ENTERPRISES



                                                     By: /s/ Fred C. Raskin
                                                     ----------------------
                                                     Title: President and COO

Attest:


By: /s/ Jean A. Scholtens
    ---------------------
    Title: Vice President and Treasurer


                                                FLEET NATIONAL BANK (FORMERLY
                                                KNOWN AS BANKBOSTON, N.A.), as
                                                Rights Agent



                                                By: /s/ Tyler Haynes
                                                    ----------------
                                                    Title: Managing Director


Attest:


By: /s/ Margaret Prentice
    ---------------------
    Title: Managing Director