Underwriting Agreement

|Effective Date: |February 04, 2002 |
|Parties: |Aphton |
|Sectors: |Biotechnology / Pharmaceuticals |
|Law Firms: |Stroock & Stroock & Lavan, White & Case |
|Governing Law: |New York |

345,000 Shares

Common Stock

($0.001 par value)

UNDERWRITING AGREEMENT

February 4, 2002

UBS Warburg LLC Morgan Keegan & Co., Inc., as Underwriters c/o UBS Warburg LLC 677 Washington Blvd. Stamford, Connecticut 06901

Ladies and Gentlemen:

Aphton Corporation, a Delaware corporation (the "Company"), proposes to issue and sell to the underwriters named in Schedule A annexed hereto (each, an "Underwriter" and collectively, the "Underwriters"), from time to time in the manner described below, an aggregate of 1,345,000 shares of common stock, $0.001 par value (the "Common Stock"), of the Company. Such shares are hereinafter collectively referred to as the "Shares." The Shares are described in the Prospectus referred to below.

The Company has filed, in accordance with the provisions of the Securities Act of 1933, as amended, and the rules and regulations thereunder (collectively called the "Act"), with the Securities and Exchange Commission (the "Commission") a registration statement on Form S-3 (File No. 333-72964) including a prospectus, relating to the Shares and the offering thereof from time to time in accordance with Rule 415 under the Act, and the Company has filed such post-effective amendments thereto as may be required prior to any sale by the Company of Shares, which incorporates by reference documents which the Company has filed in accordance with the provisions of the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder (collectively called the "1934 Act"). Such registration statement (as so amended, if applicable) has been declared effective by the Commission and is referred to herein as the "Registration Statement." The final prospectus and all applicable amendments or supplements thereto (including any pricing supplements or prospectus supplements relating to the sale of Shares from time to time), in the form first furnished to the Underwriters, are collectively referred to herein as the "Prospectus." All references to the "Registration Statement" and the "Prospectus" also shall be deemed to include all documents incorporated therein by reference pursuant to the 1934 Act; provided, that if the Company files a registration statement with the Commission pursuant to Rule 462(b) under the Act (the "Rule 462(b) Registration Statement"), then, after such filing, all references to the "Registration Statement" also shall be deemed to include the Rule 462(b) Registration Statement. A "preliminary prospectus" shall be deemed to

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refer to any prospectus used before the Registration Statement became effective and any prospectus furnished by the Company after the Registration Statement became effective which omitted information to be included in a form of prospectus filed with the Commission pursuant to Rule 424(b) under the Act. For purposes of this Agreement, all references to the Registration Statement, Prospectus or preliminary prospectus or to any amendment or supplement thereto shall be deemed to include any copy filed with the Commission pursuant to its Electronic Data Gathering, Analysis and Retrieval System ("EDGAR").

The Company and the Underwriters agree as follows:

1. Sale and Purchase. Upon the basis of the warranties and representations and subject to the terms and conditions herein set forth, the Company agrees to sell to the respective Underwriters and each of the Underwriters, severally and not jointly, agrees to purchase from the Company the aggregate number of Shares set forth opposite the name of such Underwriter in Schedule A attached hereto in each case at a purchase price of $11.938 per Share. The Company is advised by you that the Underwriters intend (i) to make a public offering of their respective portions of the Shares as soon after the effective date of the Registration Statement as in your judgment is advisable and (ii) initially to offer the Shares upon the terms set forth in the Prospectus.

2. Payment and Delivery. Payment of the purchase price for the Shares shall be made to the Company by Federal Funds wire transfer against delivery of the certificates for the Shares to you through the facilities of the Depository Trust Company (DTC) for the respective accounts of the Underwriters. Such payment and delivery shall be made at 10:00 A.M., New York City time, on February 7, 2002 (unless another time shall be agreed to by you and the Company or unless postponed in accordance with the provisions of Section 8 hereof). The time at which such payment and delivery are actually made is hereinafter sometimes called the time of purchase. Certificates for the Shares shall be delivered to you in definitive form in such names and in such denominations as you shall specify on the second business day preceding the time of purchase. For the purpose of expediting the checking of the certificates for the Shares by you, the Company agrees to make such certificates available to you for such purpose at least one full business day preceding the time of purchase.

3. Representations and Warranties of the Company. The Company represents and warrants to the Underwriters on and as of (i) the date of this Agreement and (ii) the time of purchase that:

(a) the Company meets the requirements for use of Form S-3 under the Act; the Registration Statement (including any Rule 462(b) Registration Statement) has become effective under the Act and no stop order suspending the effectiveness Registration Statement (including any Rule 462(b) Registration Statement) has been issued under the Act and no proceedings for that purpose have been instituted or are pending or, to the knowledge of the Company, are contemplated by the Commission, and any request on the part of the Commission for additional information has been complied with; the Registration Statement (including any Rule 462(b) Registration Statement) and any amendments thereto (including the filing of the Company's most recent Annual Report on Form 10-K with the Commission (the "Annual Report on Form 10-K")) comply in all material respects with the requirements of the

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Act and do not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading; each preliminary prospectus and prospectus filed as part of the Registration Statement as originally filed or as part of any amendment thereto, or filed pursuant to Rule 424 under the Act, complied when so filed in all material respects with the Act; each preliminary prospectus and the Prospectus delivered to the Underwriters for use in connection with the offering of Shares are identical to any electronically transmitted copies thereof filed with the Commission pursuant to EDGAR, except to the extent permitted by Regulation S-T; and neither the Prospectus nor any amendment or supplement thereto includes an untrue statement of a material fact or omits to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties in this subsection shall not apply to statements in or omissions from the Registration Statement or the Prospectus made in reliance upon and in conformity with information furnished to the Company in writing by the Underwriters expressly for use in the Registration Statement or the Prospectus;

(b) the documents incorporated or deemed to be incorporated by reference in the Prospectus, at the time they were or hereafter are filed with the Commission, complied and will comply in all material respects with the requirements of the 1934 Act and, when read together with the other information in the Prospectus, at the date of the Prospectus, the date of this Agreement and the time of purchase, did not and will not include an untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading;

(c) as of the date of this Agreement the Company has, and at the time of purchase will have, an authorized capitalization as set forth in the Registration Statement and the Prospectus; all of the issued and outstanding shares of capital stock of the Company, including the Common Stock, have been duly and validly authorized and issued and are fully paid and non-assessable, have been issued in compliance with all applicable laws (including, but not limited to, federal and state securities laws) and were not issued in violation of any preemptive right, resale right, right of first refusal or similar right;

(d) except as disclosed in the Registration Statement, each of the Company and each subsidiary of the Company set forth on Schedule B hereto (each a "Subsidiary" and, collectively, the "Subsidiaries") has been duly incorporated and is validly existing as a corporation and is in good standing under the laws of its respective jurisdiction of incorporation with all requisite corporate power and authority to own, lease and operate its respective properties and to conduct its respective business as conducted and as proposed to be conducted as described in the Registration Statement and Prospectus;

(e) each of the Company and the Subsidiaries is duly qualified or registered to do business as a foreign corporation in good standing in each jurisdiction in which it conducts its respective business as conducted, and as proposed to be conducted as described in the Registration Statement and Prospectus, where the ownership or leasing of its properties or the conduct of its business requires such qualification, except where the failure to so qualify, individually or in the aggregate, would not have a material adverse effect on the business,

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prospects, properties, financial condition or results of operation of the Company and the Subsidiaries, taken as a whole (a "Material Adverse Effect");

(f) the Company has no significant subsidiaries (as defined in Rule 1-02 of Regulation S-X under the Act) other than the Subsidiaries; other than the Subsidiaries the Company does not own, directly or indirectly, any shares of stock or any other equity or long-term debt securities of any corporation or have any equity interest in any firm, partnership, joint venture, association or other entity;

(g) complete and correct copies of the certificates of incorporation and of the bylaws of the Company and the Subsidiaries and all amendments thereto have been delivered to you or included in the Registration Statement, and except as set forth in the Registration Statement no changes therein will be made during the term of this agreement;

(h) except as disclosed in the Registration Statement, all of the outstanding shares of capital stock of each of the Subsidiaries have been duly authorized and validly issued, are fully paid and non-assessable and (except as otherwise described in this Section 3(h)) are owned by the Company subject to no security interest, other encumbrance or adverse claims; no options, warrants or other rights to purchase, agreements or other obligations to issue or other rights to convert any obligation into shares of capital stock or ownership interests in the Subsidiaries are outstanding;

(i) except as disclosed in the Registration Statement, the Company and each of the Subsidiaries are in compliance in all material respects with all applicable laws, orders, rules, regulations, directives, decrees and judgments;

(j) except as disclosed in the Registration Statement, neither the Company nor any of the Subsidiaries is in breach of, or in default (nor has any event occurred which with notice, lapse of time, or both would result in any breach of, or constitute a default under), under (a) its respective certificate of incorporation, charter or by-laws or (b) in the performance or observance of any obligation, agreement, covenant or condition contained in 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 or any of the Subsidiaries is a party or by which any of them or any of their properties is bound, except in the case of clause (b), for such breaches or defaults as would not reasonably be expected to have a Material Adverse Effect;

(k) the execution, delivery and performance of this Agreement, the issuance and sale of the Shares and the consummation of the transactions contemplated hereby 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 provision of the articles of incorporation, charter or by-laws of the Company or any of the Subsidiaries, or (ii) 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 or any of the Subsidiaries is a party or by which any of them or their respective properties may be bound or affected, or (iii) any federal, state, local or foreign law, regulation or rule or any decree, judgment or order

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applicable to the Company or any of the Subsidiaries, except in the case of clause (ii) for such conflicts, breaches, or defaults, individually or in the aggregate, as would not reasonably be expected to have a Material Adverse Effect;

(l) the Company has full legal right, power and authority to enter into and perform this Agreement and to consummate the transactions contemplated herein; this Agreement has been duly authorized, executed and delivered by the Company and is a legal, valid and binding agreement of the Company enforceable in accordance with its terms, except (i) as may be limited by bankruptcy, insolvency, reorganization, moratorium or similar laws affecting creditors' rights generally, or (ii) as any rights to indemnity or contribution hereunder may be limited by federal and state securities laws and public policy considerations;

(m) the capital stock of the Company, including the Shares, conforms in all material respects to the description thereof contained in the Registration Statement and Prospectus, and the certificates for the Shares (to the extent such Shares are certificated) are in due and proper form;

(n) the issuance and sale of the Shares to the Underwriters hereunder have been duly authorized by the Company; when issued and delivered against payment therefor as provided in this Agreement, the Shares will be validly issued, fully paid and non-assessable and the issuance of the Shares will not be subject to any preemptive or similar rights; except as disclosed in the Registration Statement and as to which the Company has obtained a waiver in connection with this offering, no person or entity holds a right to require or participate in the registration under the Act of the Shares pursuant to the Registration Statement; no person or entity has a right of participation or first refusal with respect to the sale of the Shares by the Company;

(o) except as disclosed in the Registration Statement and as to which the Company has obtained a waiver in connection with this offering, there are no contracts, agreements or understandings between the Company or its Subsidiaries and any person or entity granting such person or entity the right, contractual or otherwise, to cause the Company to issue to it, or register pursuant to the Act, any securities or shares of capital stock of the Company upon the issue and sale of the Shares to the Underwriters hereunder, or to require the Company to include such securities with the Shares registered pursuant to the Registration Statement, nor does any person have preemptive rights, co-sale rights, rights of first refusal or other rights to purchase any of the Shares other than those that have been expressly waived before the date hereof;

(p) the form of certificates evidencing the Shares (to the extent such Shares are certificated) complies with all applicable legal requirements and, in all material respects, with all applicable requirements of the charter and bylaws of the Company and the requirements of the NASD;

(q) no approval, authorization, consent or order of or filing with any federal, state or local governmental or regulatory commission, board, body, authority or agency is required in connection with (i) the execution, delivery and performance by the Company of this Agreement and the consummation of the transactions contemplated hereby or (ii) the sale

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and delivery of the Shares, other than (x) such as have been obtained, or will have been obtained at the time of purchase under the Act or the 1934 Act, (y) such approvals as have been obtained in connection with the approval of the listing of the Shares on the Nasdaq National Market System and (z) any necessary qualification under the securities or blue sky laws of the various jurisdictions in which the Shares are being offered by the Underwriters;

(r) Ernst & Young LLP, whose report on the consolidated financial statements of the Company and the Subsidiaries is filed with the Commission as part of the Registration Statement and Prospectus, are and were during the periods covered by their reports independent public accountants as required by the Act;

(s) each of the Company and the Subsidiaries has all necessary licenses, authorizations, consents and approvals and has made all necessary filings required under any federal, state, local or foreign law, regulation or rule, and has obtained all necessary authorizations, consents and approvals from other persons, in order to conduct its respective business, unless the failure to possess such licenses, authorizations, consents and other governmental or regulatory authorizations and approvals, individually or in the aggregate, could not reasonably be expected to have Material Adverse Effect; neither the Company nor any of the Subsidiaries is in violation of, in default under or has received any notice regarding a possible violation, default or revocation of any such license, authorization, consent or approval or any federal, state, local or foreign law, regulation or rule or any decree, order or judgment applicable to the Company or any of the Subsidiaries the effect of which could reasonably be expected to have a Material Adverse Effect;

(t) the Prospectus in paper format delivered to the Underwriters for use in connection with this offering will be identical in all material respects to the version of the Prospectus created to be transmitted to the Commission for filing via EDGAR, except to the extent permitted by Regulation S-T;

(u) all legal or governmental proceedings, contracts, leases or documents of a character required to be described in the Registration Statement or the Prospectus or to be filed as an exhibit to the Registration Statement have been so described or filed as required;

(v) except as disclosed in the Registration Statement, there are no legal or governmental proceedings pending or threatened to which the Company or any of the Subsidiaries or any of their respective officers is a party or of which any of their respective properties is subject at law or in equity, or before or by any federal, state, local or foreign governmental or regulatory commission, which, if determined adversely to the Company or any of its Subsidiaries, could result in a judgment, decree or order which could reasonably be expected to have a Material Adverse Effect or prevent consummation of the transactions contemplated hereby;

(w) the consolidated financial statements of the Company and the Subsidiaries included in the Registration Statement and the Prospectus present fairly in all material respects the consolidated financial position of the Company and the Subsidiaries as of the dates indicated and the consolidated results of operations and cash flows of the Company and

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the Subsidiaries for the periods specified; such financial statements have been prepared in conformity with generally accepted accounting principles as applied in the United States and on a consistent basis during the periods involved and in accordance with Regulation S-X promulgated by the Commission; the financial statement schedules included or incorporated by reference in the Registration Statement and the Prospectus fairly present in all material respects the information required to be shown therein; no other financial statements or schedules are required by Form S-3 or otherwise to be included in the Registration Statement or Prospectus; any pro forma financial statements and other pro forma financial information included in the Registration Statement and the Prospectus present fairly the information shown therein, have been prepared in accordance with the Commission's rules and guidelines for pro forma financial statements, have been properly compiled on the pro forma bases set forth therein and, in the opinion of the Company, the assumptions used in the preparation thereof are reasonable and the adjustments used therein are appropriate to reflect the transaction or circumstances referred to therein;

(x) subsequent to the respective dates as of which information is given in the Registration Statement and the Prospectus, there has not been (i) any material adverse change, or any development involving a prospective material adverse change, in the business, prospects, properties or assets described or referred to in the Registration Statement, or the results of operations, condition (financial or otherwise), business or operations of the Company and the Subsidiaries, whether or not arising in the ordinary course of business, or (ii) any transaction which is material to the Company or the Subsidiaries, planned or entered into by the Company or any of the Subsidiaries, or (iii) any obligation, direct or contingent, which is material to the Company and the Subsidiaries, incurred by the Company or the Subsidiaries, except obligations incurred in the ordinary course of business, or (iv) any change in the capital stock or outstanding indebtedness of the Company or the Subsidiaries, or (v) any dividend or distribution of any kind declared, paid or made on the capital stock of the Company. Neither the Company nor the Subsidiaries has any material contingent obligation which is not disclosed in the Registration Statement;

(y) the Company has filed in a timely manner all reports required to be filed pursuant to Sections 13, 14, 15(d) of the 1934 Act during the preceding twelve calendar months and if during such period the Company has relied on Rule 12b-25(b) under the 1934 Act ("Rule 12b-25(b)") with respect to a report or a portion of a report, that report or portion of a report has actually been filed within the time period prescribed by Rule 12b-25(b);

(z) the Company is not and, after giving effect to the offering and sale of the Shares, will not be an "investment company" or an entity "controlled" by an "investment company," as such terms are defined in the Investment Company Act of 1940, as amended (the "Investment Company Act");

(aa) except as disclosed in the Prospectus, there are no outstanding (i) securities or obligations of the Company or any of its Subsidiaries convertible into or exchangeable for any capital stock of the Company or any such Subsidiary, or (ii) warrants, rights or options to subscribe for or purchase from the Company or any such Subsidiary any such capital stock or any such convertible or exchangeable securities or obligations, or (iii) obligations

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of the Company or any such Subsidiary to issue any shares of capital stock, any such convertible or exchangeable securities or obligation, or any such warrants, rights or options;

(bb) each of the Company, the Subsidiaries, and each of their respective officers, directors and controlling persons has not taken, and will not take, directly or indirectly, any action which is designed to or which has constituted or which might reasonably be expected to cause or result in stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Shares;

(cc) the Company (i) is not required to register as a "broker" or "dealer" in accordance with the provisions of the 1934 Act or the rules and regulations thereunder, and (ii) directly, or indirectly through one or more intermediaries, does not control any member firm of the NASD;

(dd) the Company has not relied upon the Underwriters or legal counsel for the Underwriters for any legal, tax or accounting advice in connection with the offering and sale of the Shares;

(ee) any certificate signed by any officer of the Company or any Subsidiary delivered to the Underwriters or to counsel for the Underwriters pursuant to or in connection with this Agreement shall be deemed a representation and warranty by the Company to the Underwriters as to the matters covered thereby;

(ff) to the Company's knowledge, all agreements between the Company or any of the Subsidiaries and third parties expressly referenced in the Prospectus are legal, valid and binding obligations of the Company or one or more of the Subsidiaries, enforceable in accordance with their respective terms, except to the extent enforceability may be limited by bankruptcy, insolvency, reorganization, moratorium or similar laws affecting creditors' rights generally and by general principles of equity;

(gg) no relationship, direct or indirect, exists between or among the Company or any of the Subsidiaries, on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company or any of the Subsidiaries, on the other hand, which is required by the Act to be described in the Registration Statement and the Prospectus that is not so described;

(hh) with such exceptions as could not reasonably be expected to have a Material Adverse Effect on the Company and the Subsidiaries, taken as a whole, the Company and the Subsidiaries have good and marketable title in fee simple to all real property, if any, and good title to all personal property owned by them, in each case free and clear of all liens, security interests, pledges, charges, encumbrances, mortgages and defects, except such as are disclosed in the Prospectus or such as do not materially and adversely affect the value of such property and do not interfere with the use made or proposed to be made of such property by the Company and the Subsidiaries; and any real property and buildings held under lease by the Company or any Subsidiary are held under valid, existing and enforceable leases, with such exceptions as are disclosed in the Prospectus or are not material and do not interfere with the use made or proposed to be made of such property and buildings by the Company or such Subsidiary;

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(ii) the Company and the Subsidiaries have ownership or license or legal right to use all material patent, copyright, trade secret and trademark rights known by it to be necessary to the conduct of the business of the Company and the Subsidiaries as now conducted (collectively, "Intellectual Property") other than Intellectual Property generally available on commercial terms from other sources;

(jj) all material licenses or other material agreements under which (i) the Company and the Subsidiaries are granted rights in Intellectual Property, other than Intellectual Property generally available on commercial terms from other sources, and (ii) the Company or any Subsidiary has granted rights to others in Intellectual Property owned or licensed by the Company or the Subsidiaries, are in full force and effect and there is no material default by the Company or any Subsidiary or, to the Company's knowledge, any other party thereto; ...