Exhibit 8B
                                            ----

                    [Letterhead of Nutter, McClennen & Fish, LLP]
   
                                   April 27, 1998
    


Somerset Savings Bank
212 Elm Street
Somerville, MA  02144

     Re:  UST Corp. Registration Statement on Form S-4

Ladies and Gentlemen:

     In connection with the above-referenced registration statement (the
"Registration Statement") regarding the proposed merger (the "Transaction") of
Somerset Savings Bank, a Massachusetts-chartered stock savings back ("Somerset")
into USTrust, a Massachusetts-charted bank and trust company ("USTrust"),
pursuant to the Affiliation Agreement and Plan of Reorganization, dated as of
December 9, 1997 by and between Somerset and UST Corp. ("UST"), and joined in
and ratified by Mosaic Corp., a wholly-owned subsidiary of UST ("Mosaic"), on
January 9, 1998 (the "Affiliation Agreement"), you have requested our opinion
regarding certain federal income tax matters related to the parties to the
Transaction.  Capitalized terms used in this letter and not otherwise defined
herein have the meaning assigned to such terms in the Registration Statement or
the Affiliation Agreement.

     The opinion set forth in this letter is based on relevant provision of the
Internal Revenue Code of 1986, as amended (the "Code"), Treasury Regulations
thereunder (including proposed and temporary Treasury Regulations) and
interpretations of the foregoing as expressed in court decisions, administrative
determinations, and the legislative history as of the date hereof.  These
provisions and interpretations are subject to change, which may or may not be
retroactive in effect, that might result in modifications of our opinion.

     In rendering our opinion we examined such records, documents and other
materials as we considered necessary or appropriate as a basis for such opinion,
including the Affiliation Agreement, the Registration Statement (including all
amendments made through the date hereof) and such other documents and
information provided by UST, USTrust, Mosaic and Somerset as we deemed relevant
to our opinion.

     UST, USTrust, Mosaic and Somerset have each provided us with a certificate
(the "Officers' Certificates"), executed by their duly appointed officers,
respectively, setting forth certain representations relating to the Transaction
and the manner in which UST, USTrust, Mosaic and Somerset have been owned and
operated prior to the Transaction, and will be 



owned and operated after the Transaction.  We have also relied on the 
statements in the Registration Statement, the Affiliation Agreement and other 
documents relating to the Transaction (collectively with the Registration 
Statement and the Affiliation Agreement, the "Documents") regarding the 
operation and ownership of UST, USTrust, Mosaic and Somerset.  We have 
neither independently investigated nor verified such representations or 
statements, and we assume that such representations and statements are true, 
correct and complete and that all representations made "to the best of the 
knowledge and belief" of any person or party or with similar qualification 
are and will be true, correct and complete as if made without such 
qualification and that no action will occur from the date hereof until the 
Transaction that is inconsistent with such representations.

     We have assumed for the purposes of this opinion that:  (1)  the 
Transaction and related transactions contemplated by the Documents will be 
consummated in accordance with the Documents and as described in the 
Registration Statement (including satisfaction of all covenants and 
conditions therein without amendment or waiver thereof);  (2)  UST, USTrust, 
Mosaic, Somerset and any affiliated entities, have operated and will operate 
in accordance with their governing documents and applicable laws.  We confirm 
to you, however, that we are not aware of any facts that would lead us to 
believe that any of these assumptions is false in any material way.

     We have also assumed in rendering the opinion set forth herein:  (1) the
genuineness of all signatures on documents we have examined;  (2)  the
authenticity of all documents submitted to us as originals;  (3)  the conformity
to the original documents of all documents submitted to us as copies;  (4)  the
conformity of final documents to all documents submitted to us as drafts;  (5) 
the authority and capacity of the individual or individuals who executed any
such documents on behalf of any person;  (6)  the accuracy and completeness of
all records made available to us;  (7)  the factual accuracy of all
representations, warranties and other statements made by all parties;  and (8) 
the continued accuracy of all documents, certificates, warranties and covenants
on which we have relied in rendering the opinion set forth below and that were
given or dated earlier than the date of this letter, insofar as relevant to the
opinion set forth herein, from such earlier date through and including the date
of this letter.

     Based upon and subject to the foregoing, we are of the opinion that:

   
     1.   The Transaction would be treated for federal income tax purposes as
an acquisition by Mosaic of substantially all the assets of Somerset solely in
exchange for the stock of UST (the "Consideration") and the assumption of
Somerset's liabilities, followed by the transfer of such assets, subject to such
liabilities, to USTrust.
    

   
     2.   The acquisition by Mosaic of substantially all the assets of Somerset
solely in exchange for the Consideration and the assumption of Somerset's
liabilities, as described above, would constitute a reorganization within the
meaning of Section 368(a)(1)(C) of the Code.  For purposes of this Opinion,
"substantially all" means at least 90% of the fair market value of the net
assets and at least 70% of the fair market value of the gross assets of
Somerset.
    



   
     3.   UST, Mosaic and Somerset would each be a "party to a reorganization"
within the meaning of Section 368(b) of the Code.
    

   
     4.   Pursuant to Section 368(a)(2)(C) of the Code, the acquisition by
Mosaic of substantially all the assets of Somerset would not be disqualified as
a reorganization under Section 368(a)(1)(C) of the Code by reason of the fact
that the assets of Somerset that are acquired by Mosaic are transferred to
USTrust.
    

   
     5.   No gain or loss would be recognized by Somerset on the transfer of
substantially all its assets to Mosaic solely in exchange for the Consideration
and the assumption of Somerset's liabilities.
    

   
     6.   No gain or loss would be recognized by Somerset on the distribution
to its shareholders of the Consideration in pursuance of the plan of
reorganization.
    

   
     7.   No gain or loss would be recognized by the shareholders of Somerset
upon the receipt of Consideration (including fractional shares deemed received
as described in paragraph 10 below) solely in exchange for their shares of
Somerset stock.
    

   
     8.   The basis of the Consideration to be received by the shareholders of
Somerset (including fractional shares deemed received as described in paragraph
below) would be the same as the basis of the Somerset stock surrendered in
exchange therefor.
    

   
     9.   The holding period of the Consideration to be received by the
shareholders of Somerset (including fractional shares deemed received as
described in paragraph 10 below) would include the holding period of the
Somerset stock surrendered in exchange therefor, provided the Somerset stock was
held as a capital asset by the applicable shareholder of Somerset on the date of
the exchange.
    

   
     10.  The payment of cash to Somerset shareholders in lieu of fractional
share interests of UST would be treated for federal income tax purposes as if
the fractional shares were distributed as part of the exchange and then were
redeemed by UST.  These cash payments would be treated as distributions in full
payment in exchange for the stock redeemed as provided in Section 302(a) of the
Code.
    

   
     Other than as expressly stated above, we express no opinion on any issue 
relating to UST or to any investment therein. In particular, our opinion 
addresses the matters set forth above under U.S. federal income tax law only, 
and no opinion is expressed under the provisions of any foreign state, or 
local tax law. Further, without our express written consent, the opinion 
expressed herein may not be relied upon by any persons other than those to 
whom it is addressed.
    

   
     We hereby consent to the filing of this opinion as an exhibit to the 
Registration Statement and to the use of the name of our firm therein and 
under the caption "Legal Opinions" in the Registration Statement.
    

                                             Respectfully submitted,


   
                                             /s/ Nutter, McClennen & Fish, LLP
                                             ---------------------------------
                                             [NUTTER, McCLENNEN & FISH, LLP]