SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                             ----------------------

                                   FORM 8-A/A

                                 Amendment No. 4

                FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                    PURSUANT TO SECTION 12(b) OR 12(g) OF THE
                         SECURITIES EXCHANGE ACT OF 1934


                                NBT BANCORP INC.
  ----------------------------------------------------------------------------
             (Exact name of registrant as specified in its charter)


        Delaware                      0-14703                    16-1268674
- ------------------------   -------------------------------     ---------------
(State of incorporation          Commission File No.          (I.R.S. Employer
    or organization)                                         Identification No.)


                 52 South Broad Street, Norwich, New York 13815
                 -----------------------------------------------
              (Address of principal executive offices and zip code)



Securities to be registered pursuant to Section 12(b) of the Act:

   Title of each class                         Name of each exchange on which
   to be so registered                         each class is to be registered
   -------------------                         ------------------------------

            None                                        Not Applicable


Securities to be registered pursuant to Section 12(g) of the Act:

            Share Purchase Rights Pursuant to Stockholder Rights Plan
           -----------------------------------------------------------
                                (Title of Class)





ITEM 1.  DESCRIPTION OF REGISTRANT'S SECURITIES TO BE REGISTERED.

         On November 15, 1994, the Board of Directors of the Registrant declared
a dividend  distribution of one Right for each outstanding share of Registrant's
common stock to  stockholders of record at the close of business on November 15,
1994. See the Registrant's Form 8-A, dated November 29, 1994,  Registrant's Form
8-A/A,  Amendment No. 1, dated December 21, 1999, and  Registrant's  Form 8-A/A,
Amendment  No. 2, dated  February 24, 2000,  for a complete  description  of the
Rights  Agreement (the "Rights  Agreement")  between the Registrant and American
Stock Transfer Trust Company,  as Rights Agent (the "Rights Agent") , as amended
as  of  December  16,  1999.  Since  adoption  of  the  Rights  Agreement,   new
certificates for the  Registrant's  common stock issued after November 15, 1994,
contained a notation incorporating the Rights Agreement by reference.

         On April  19,  2000,  the  Registrant  and BSB  Bancorp,  Inc.  ("BSB")
executed an Agreement and Plan of Merger (the "Merger Agreement") providing for,
among other things,  the merger of BSB with and into  Registrant.  In connection
with the execution of the Merger Agreement, the Registrant executed an amendment
(the  "Amendment")  to the Rights  Agreement in order to amend the definition of
"Acquiring Person" set forth in the Rights Agreement to provide that neither BSB
nor any  affiliated  or  associated  party  (collectively  with  BSB,  the  "BSB
Parties")  will be deemed to be an  Acquiring  Person by virtue of the fact that
BSB is the  Beneficial  Owner (as  defined  in the Rights  Agreement)  solely of
shares of  Registrant  common stock (i) of which any BSB Party is or becomes the
Beneficial Owner by reason of the approval,  execution or delivery of the Merger
Agreement or the Stock Option Agreement, dated as of April 19, 2000, between the
Registrant, as issuer, and BSB, as grantee (the "Stock Option Agreement"), or by
reason  of  the  consummation  of any  transaction  contemplated  in the  Merger
Agreement,  the Stock Option  Agreement or both,  (ii) of which any BSB Party is
the Beneficial  Owner on April 19, 2000, (iii) acquired in satisfaction of debts
contracted prior to April 19, 2000, in good faith in the ordinary course of such
BSB  Party's  banking  business,  (iv)  held by any  BSB  Party  in a bona  fide
fiduciary or depository capacity or (v) owned in the ordinary course of business
by either (A) an investment  company registered under the Investment Company Act
of 1940, as amended,  or (B) an investment account, in either case for which any
BSB Party acts as investment advisor.

         The Rights may have  certain  anti-takeover  effects.  The Rights  will
cause  substantial  dilution  to a person or group that  attempts to acquire the
Registrant  without  conditioning  the offer on a  substantial  number of Rights
being  acquired.  However,  the Rights should not  interfere  with any merger or
other  business  combination  approved by the Board of Directors.  A copy of the
Rights  Agreement  between the  Registrant  and the Rights Agent  specifying the
terms  of the  Rights  is  incorporated   herein  by  reference.  The  foregoing
description  of the Rights does not purport to be complete  and is  qualified in
its entirety by reference to the Rights Agreement, as amended.

         ITEM 2.  EXHIBITS.

         2.1      Agreement  and Plan of Merger,  dated as of April 19, 2000, by
                  and  between  NBT  Bancorp   Inc.   and  BSB   Bancorp,   Inc.
                  (incorporated  by reference to Exhibit 2.1 to Form 8-K,  dated
                  as of April 19, 2000, of NBT Bancorp Inc., File No. 0-14703).

         2.2      BSB Stock  Option  Agreement,  dated  April 19,  2000,  by and
                  between BSB Bancorp,  Inc. as "Issuer" and NBT Bancorp Inc. as
                  "Grantee" is part of the Agreement  and Plan of Merger,  which
                  is filed as Exhibit 2.1 above.

         4.1      Rights Agreement,  dated as of November 15, 1994,  between NBT
                  Bancorp Inc.  and American  Stock  Transfer  Trust  Company as
                  Rights Agent (incorporated  herein by reference to Exhibit 4.1
                  of the  Registrant's  Form 8-A, dated November 25, 1994,  File
                  No. 0-14703).

         4.2      Amendment to Rights  Agreement,  dated as of December 16, 1999
                  between NBT Bancorp  Inc. and American  Stock  Transfer  Trust
                  Company as Rights Agent  (incorporated  herein by reference to
                  Exhibit 4.2 of the Registrant's  Form 8-A/A,  Amendment No. 1,
                  dated December 21, 1999, File No. 0-14703).





         4.3      Second  Amendment to Rights  Agreement,  dated as of April 19,
                  2000,  between NBT Bancorp Inc. and  American  Stock  Transfer
                  Trust Company as Rights Agent (filed herewith).









                                   SIGNATURES

         Pursuant to the  requirements of Section 12 of the Securities  Exchange
Act of 1934, the Registrant  has duly caused this  registration  statement to be
signed on its behalf by the undersigned, thereunto duly authorized.

                                     NBT BANCORP INC.

                                     By:
                                            Michael J. Chewens
                                            Executive Vice President and Chief
                                              Financial Officer

Date:    May 23, 2000










                                  EXHIBIT INDEX

         4.3      Second  Amendment to Rights  Agreement,  dated as of April 19,
                  2000,  between NBT Bancorp Inc. and  American  Stock  Transfer
                  Trust Company as Rights Agent (filed herewith).





                                   EXHIBIT 4.3

  SECOND AMENDMENT TO RIGHTS AGREEMENT, DATED AS OF APRIL 19, 2000, BETWEEN NBT
    BANCORP INC. AND AMERICAN STOCK TRANSFER TRUST COMPANY AS RIGHTS AGENT.


                      SECOND AMENDMENT TO RIGHTS AGREEMENT

         SECOND AMENDMENT dated as of April 19, 2000 (this "Second  Amendment"),
to the RIGHTS AGREEMENT dated as of November 15, 1994, as amended as of December
16, 1999 (the  "Agreement"),  between NBT Bancorp  Inc., a Delaware  corporation
(the  "Corporation"),  and American  Stock  Transfer  Trust Company (the "Rights
Agent").

         WHEREAS,  the Corporation and the Agent have entered into the Agreement
at the direction of the Corporation; and

         WHEREAS,  the  Distribution  Date (as defined in the Agreement) has not
occurred and the  penultimate  sentence of Section 26(a) of the Agreement is not
applicable to this Amendment; and

         WHEREAS,   Section  27  of  the  Rights  Agreement  provides  that  the
Corporation  may from time to time  supplement or amend the Rights  Agreement in
accordance with the terms of Section 27; and

         WHEREAS, the Corporation and BSB Bancorp,  Inc., a Delaware corporation
("BSB"),  have entered into an Agreement  and Plan of Merger,  dated as of April
19,  2000  (the  "Merger  Agreement"),  pursuant  to which BSB will  merge  (the
"Merger") with and into the Corporation; and

         WHEREAS,  in connection with the Merger Agreement,  the Corporation and
BSB have  entered  into a Stock  Option  Agreement,  dated  April 19,  2000 (the
"Option  Agreement"),  pursuant to which the  Corporation  has granted to BSB an
option to  purchase  shares of the  Corporation's  Common  Stock  under  certain
circumstances and upon certain terms and conditions; and

         WHEREAS,  the Board of Directors has determined  that the  transactions
contemplated by the Merger Agreement are advisable; and

         WHEREAS,  the Board of Directors has determined that it is advisable to
amend the Rights Agreement to exempt the Merger Agreement,  the Option Agreement
and the transactions  contemplated thereby (including,  without limitation,  the
option granted  pursuant to the Option  Agreement)  from the  application of the
Rights Agreement; and

         WHEREAS,  the Board of  Directors of the  Corporation  has approved and
adopted  this  Amendment  and  directed  that  the  proper   officers  take  all
appropriate steps to execute and put into effect this Amendment.

         NOW, THEREFORE, the Agreement is amended as follows (terms used and not
defined herein have the meanings as defined in the Agreement):

 1.               Section  1(a) of the  Rights  Agreement  is hereby  amended by
                  inserting the following sentence at the end thereof:

                  "Notwithstanding  anything in this  Agreement to the contrary,
         until the  termination  of both the BSB  Merger  Agreement  and the BSB
         Stock Option Agreement (each as defined below) in accordance with their
         respective  terms,  neither BSB Bancorp,  Inc., a Delaware  corporation
         ("BSB"),  nor any Affiliate or Associate of BSB (collectively with BSB,
         the "BSB Parties") shall be deemed to be an Acquiring  Person by virtue
         of the fact that BSB is the Beneficial Owner solely of shares of Common
         Stock (i) of which any BSB Party is or becomes the Beneficial  Owner by
         reason of the



         approval,  execution or delivery of the  Agreement  and Plan of Merger,
         dated as of April 19, 2000, by and between the  Corporation and BSB, as
         may be amended from time to time (the "BSB Merger  Agreement"),  or the
         Stock Option Agreement,  dated April 19, 2000, between the Corporation,
         as issuer,  and BSB,  as grantee,  as may be amended  from time to time
         (the "BSB Stock Option Agreement"), or by reason of the consummation of
         any transaction contemplated in the BSB Merger Agreement, the BSB Stock
         Option Agreement or both, (ii) of which any BSB Party is the Beneficial
         Owner on the date  hereof,  (iii)  acquired  in  satisfaction  of debts
         contracted  prior to the date  hereof by any BSB Party in good faith in
         the ordinary course of such BSB Party's banking business,  (iv) held by
         any BSB Party in a bona fide fiduciary or depository  capacity,  or (v)
         owned in the  ordinary  course of business by either (A) an  investment
         company  registered  under  the  Investment  Company  Act of  1940,  as
         amended, or (B) an investment account, in either case for which any BSB
         Party acts as investment advisor."

 2.               Section 15 of the Rights  Agreement  is hereby  amended to add
                  the following sentence at the end thereof:

                  "Nothing  in this  Agreement  shall be  construed  to give any
         holder of Rights or any other  Person  any legal or  equitable  rights,
         remedies  or  claims  under  this  Agreement  in  connection  with  any
         transactions  contemplated by the BSB Merger Agreement or the BSB Stock
         Option Agreement."

 3.               This  Amendment  shall be deemed to be in force and  effective
                  immediately  prior to the execution and delivery of the Merger
                  Agreement.  Except as amended  hereby,  the  Rights  Agreement
                  shall  remain in full force and effect and shall be  otherwise
                  unaffected hereby.

 4.               The  provisions  of  Sections  27,  29,  30, 31, and 33 of the
                  Agreement  shall  apply  to  this  Amendment  as if set  forth
                  herein.


         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the day and year first above written.

                     NBT BANCORP INC.

                     By:    /s/  DARYL R. FORSYTHE
                          ----------------------------------
                                 Daryl R. Forsythe
                              President and Chief Executive Officer



                     AMERICAN STOCK TRANSFER TRUST COMPANY, as
                     Rights Agent

                     By:     /s/  HERBERT J. LEMMER
                          -----------------------------------
                                  Herbert J. Lemmer
                                     Vice President