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                                                                 EXHIBIT 5
UST

March 25, 1994

UST Corp.
40 Court Street
Boston, Massachusetts 02108

Re: UST Corp. - Registration Statement on Form S-3
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Gentlemen:

As Executive Vice President, General Counsel and Clerk to UST Corp., a
Massachusetts corporation (the "Company"), I have acted as counsel to the
Company in connection with the registration of an aggregate of 500,000 shares
of the Company's common stock, par value $0.625 per share (the "Common Stock"),
pursuant to a Registration Statement on Form S-3 (the "Registration
Statement"). All of the shares of Common Stock to be registered under the
Registration Statement are currently outstanding unregistered shares of the
Company's Common Stock. The shares of Common Stock are expected to be sold by
Kidder, Peabody Group, Inc. and the Company will receive no part of the
proceeds of such sale.

In rendering the opinion set forth below, I have examined certain corporate
records of the Company, including its Restated Articles of Organization, as
amended, its By-laws, minutes of meetings of its Board of Directors and
stockholders and such other documents, instruments and certificates of
government officials and officers of the Company as I have deemed necessary.

I have made such examination of Massachusetts law as I have deemed relevant for
purposes of this opinion, but have not made any review of the laws of any other
state or jurisdiction. Accordingly, this opinion is limited to Massachusetts
law.

Based upon and subject to the foregoing, I am of the opinion that the Common
Stock being registered pursuant to the Registration Statement is duly
authorized, validly issued, fully paid and nonassessable.

I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and I further consent to the reference to me under the
caption "Legal Opinion", in the Registration Statement.

                                        Very truly yours,

                                        /s/ Eric R. Fischer 
                                        Eric R. Fischer 
                                        General Counsel and Clerk