December 19, 2001





UBS Warburg LLC
677 Washington Boulevard
Stamford, Connecticut 06901


Re:      Aphton Corporation

Ladies and Gentlemen:

     We have acted as special counsel for Aphton Corporation, a Delaware
corporation ("the Company"), in connection with (i) the execution and delivery
of a Distribution Agreement, dated December __, 2001 (the "Distribution
Agreement"), between the Company and UBS Warburg LLC (the "Agent"), providing
for the purchase by or through the Agent from the Company, upon the terms and
conditions set forth in the Distribution Agreement, of up to 1,500,000 shares of
the Company's Common Stock, par value $.001 per share (the "Shares"), and (ii)
the preparation and filing by the Company with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Act") of the Registration Statement on Form S-3 (File No. 333-72964). As
described in the Prospectus, the Company's Annual Report on Form 10-K/A for the
year ended January 31, 2001, its Quarterly Reports on Form 10-Q for the five
months ended June 30, 2001 and eight months ended September 30, 2001, its
Current Report on Form 8-K dated March 16, 2001 and the description of the
Company's Common Stock contained in the Company's Registration Statement on Form
8-A, filed with the Commission on January 30, 1998 (collectively, the
"Incorporated Documents"), are incorporated in the Prospectus by reference.

     In so acting, we have examined such certificates of public officials, and
certificates of officers of the Company, and the originals (or copies thereof
certified to our satisfaction) of such corporate documents and records of the
Company, and such other documents, records and papers as we have deemed relevant
in order to give the opinions hereinafter set forth. In this connection, we have
assumed the genuineness of signatures on, the authenticity of all documents
submitted to us as originals and the conformity to authentic original documents
of all documents submitted to us as certified, conformed or photostatic copies.
Also, we have relied upon such certificates of public officials, and officers of
the Company and such other certifications with respect to the accuracy of
material factual matters contained therein which were not independently
established. We did not participate in the preparation of the Incorporated
Documents or review any of them prior to their being filed with the Commission
under the


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Securities Exchange Act of 1934, as amended (the "Exchange Act"), but we did
review them in connection with our participation in the preparation of the
Prospectus.

     Based upon and subject to the foregoing, it is our opinion that:

          1. The Company has been duly incorporated and is validly existing as a
     corporation in corporate good standing under the laws of the State of
     Delaware and has the corporate power and authority to own, lease and
     operate its properties and conduct its business as described in the
     Registration Statement, to enter into the Distribution Agreement, to issue,
     sell and deliver the Shares and to consummate the transactions contemplated
     in the Prospectus.

          2. The Common Stock of the Company, including the Shares, conforms in
     all material respects to the description thereof contained in the
     Registration Statement and the Prospectus.

          3. The Shares have been duly and validly authorized by the Company for
     offer, sale, issuance and delivery pursuant to the Distribution Agreement
     and, when issued and delivered against payment therefor as provided in the
     Distribution Agreement, will be duly and validly issued and fully paid and
     non-assessable.

          4. To our knowledge, the Company is duly qualified to do business as a
     foreign corporation and is in good standing in each jurisdiction where the
     ownership or leasing of its properties or the conduct of its business
     requires such qualification, except where the failure to so qualify would
     not have a material adverse effect on the business, properties, financial
     condition or results of operation of the Company taken as a whole (a
     "Material Adverse Effect").

          5. To our knowledge and other than as set forth in the Prospectus,
     there is no legal or governmental proceeding threatened in writing or
     pending in any state or federal court located in the County of New York or
     State of New York, to which the Company is a party or to which any property
     of the Company is subject, which could prevent consummation of the
     transactions contemplated by the Distribution Agreement.

          6. The Distribution Agreement has been duly authorized, executed and
     delivered by the Company.

          7. The execution, delivery and performance of the Distribution
     Agreement, the issuance and sale of the Shares and the consummation of the
     transactions contemplated by the Distribution Agreement will not conflict
     with, or result in any breach of or constitute a default under (nor
     constitute any event which with notice, lapse of time, or both would result
     in any breach of, or constitute a default under), (i) any provisions of the
     charter or by-laws of the Company or, (ii) to our knowledge, under any
     provision of any license, indenture, mortgage, deed of trust, bank loan or
     credit agreement or other evidence of indebtedness, or any lease, contract
     or other agreement or instrument to which the Company is a party or by
     which it or its property may be bound or affected and which have been filed
     by the Company with the Commission under the Exchange Act, and are listed
     in the exhibit index to the Company's most recent Annual Report on Form

                                      -2-
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     10-K/A or were subsequently filed prior to the date hereof under the
     Exchange Act, or (iii) under any decree, judgment or order known to us to
     be applicable to the Company or under any U.S. Federal or New York State
     law, regulation or rule which in our experience are normally applicable to
     transactions of the type contemplated by the Purchase Agreement, except in
     the case of clauses (ii) and (iii) for such conflicts, breaches, or
     defaults, individually or in the aggregate, as would not reasonably be
     expected to have a Material Adverse Effect.

          8. No approval, authorization, consent or order of or filing with any
     New York State or U.S. Federal governmental agency or body or any New York
     State or U.S. Federal court is required to be obtained or made by the
     Company for the issuance and sale of the Shares or the consummation by the
     Company of the transactions as contemplated by the Distribution Agreement
     except such as may be required by the Act and the applicable rules and
     regulations thereunder, the securities or blue sky laws of the various
     jurisdictions in which the Shares are being offered by the Agent (as to
     which we express no opinion) or under the rules and regulations of the
     National Association of Securities Dealers, Inc. (as to which we express no
     opinion).

          9. The Company is not and, after giving effect to the offering and
     sale of the Shares, will not be required to register as an "investment
     company" as such term is defined in the Investment Company Act of 1940, as
     amended.

     In passing upon the form of the Registration Statement and the Prospectus,
we necessarily have assumed the accuracy and completeness of the information
included or incorporated by reference therein by the Company and the
responsiveness to the applicable forms, rules and regulations of the Commission
promulgated under the Exchange Act of the information included in the
Incorporated Documents by the Company and we take no responsibility therefor.
Based upon such assumptions, in our opinion the Registration Statement, as of
its effective date, and the Prospectus, as of its date (except in each case for
the financial statements and schedules and other financial and statistical data
contained or incorporated by reference therein or omitted therefrom, as to which
we express no opinion), appeared on their face to comply as to form in all
material respects with the requirements of the Act and the rules and regulations
of the Commission thereunder.

     In the course of the preparation by the Company of the Registration
Statement and the Prospectus (other than the Incorporated Documents), we have
participated in conferences with certain officers of the Company, with
representatives of the independent auditors of the Company, and with you and
your counsel. Based upon such participation in the preparation of the
Registration Statement and the Prospectus (other than the Incorporated
Documents) and our review and discussion of the contents thereof, but without
independent check or verification except as otherwise specified above, nothing
has come to our attention which causes us to believe that the Registration
Statement, as of its effective date, or the Prospectus, as of its date, (except
in each case for the financial statements and schedules and other financial or
statistical data contained or incorporated by reference therein or omitted
therefrom as to which we express no belief), contained any untrue statement of a
material fact or omitted therefrom to state any material fact required to be
stated therein or necessary to make the statements therein (in the case of the
Prospectus, in the light of the circumstances under which they were made) not
misleading.

                                      -3-
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     The opinions expressed above are limited to questions arising under the
Federal Law of the United States, the General Corporation Law of the State of
Delaware and the law of the State of New York. This opinion may not be relied
upon by or published or communicated to any person and may not be used for any
other purpose whatsoever without prior written approval in each instance.

     We consent to the filing of this opinion as an exhibit to the Registration
Statement and to the reference to our firm appearing under the caption "Legal
Matters" in the Prospectus forming Part of the Registration Statement. In giving
this consent, we do not thereby admit that we are within the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission.



                                                     Very truly yours,

                                                     /s/ WHITE & CASE LLP

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