Document:

EXHIBIT 10.32
                                                                  --------------

                    CONFIDENTIAL TREATMENT HAS BEEN REQUESTED
                          FOR PORTIONS OF THIS EXHIBIT

                        DEVELOPMENT AND LICENSE AGREEMENT

                                     BETWEEN

                     BOEHRINGER INGELHEIM INTERNATIONAL GMBH

                                       AND

                           VION PHARMACEUTICALS, INC.

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                                TABLE OF CONTENTS

ARTICLE 1.  DEFINITIONS...................................................... 1
ARTICLE 2.  RESEARCH AND DEVELOPMENT......................................... 5
ARTICLE 3.  DISTRIBUTION & LICENSE RIGHTS.................................... 7
ARTICLE 4.  PAYMENT OBLIGATIONS.............................................. 9
ARTICLE 5.  PAYMENT; RECORDS, AUDITS.........................................10
ARTICLE 6.  INTELLECTUAL PROPERTY RIGHTS AND INFRINGEMENT....................11
ARTICLE 7.  CONFIDENTIALITY..................................................13
ARTICLE 8.  REPRESENTATIONS, WARRANTIES AND COVENANTS........................14
ARTICLE 9.  INDEMNITY........................................................16
ARTICLE 10. TRANSITION.......................................................17
ARTICLE 11. TERM AND TERMINATION.............................................18
ARTICLE 12. MISCELLANEOUS....................................................19

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                        DEVELOPMENT AND LICENSE AGREEMENT
                        ---------------------------------

         THIS AGREEMENT is entered into as of December 1, 1999 (the "Effective
Date"), by and between BOEHRINGER INGELHEIM INTERNATIONAL GmbH, a limited
liability company organized under the laws of Germany having its principal place
of business at D-55216 Ingelheim, Rhein, Germany ("BI") and VION
PHARMACEUTICALS, INC., a Delaware corporation having offices at Four Science
Park, New Haven, Connecticut 06511 ("Vion").

         WHEREAS, the parties have entered a Collaborative Development and
Distribution Agreement relative to the development and commercialization of
Promycin(R)(porfiromycin) dated November 24, 1997 (hereafter "Original
Agreement"); and

         WHEREAS, the parties seek to redefine the allocation of responsibility
under the Original Agreement to facilitate the development and commercialization
of Promycin(R); and

         WHEREAS, the parties now seek a new agreement to define, among other
things, the responsibilities assumed by BI relating to the development and
commercialization of Promycin(R).

         NOW, THEREFORE, the parties agree as follows:

                             ARTICLE 1. DEFINITIONS
                             ----------------------

         As used herein, the following terms shall have the following meanings:

         1.1  "Affiliate" means an individual, trust, business trust, joint
venture, partnership, corporation, limited liability company, association or any
other entity which owns, is owned by or is under common ownership with a party.
For the purposes of this definition, the term "owns" (including, with
correlative meanings, the terms "owned by" and "under common ownership with") as
used with respect to any party, shall mean the possession (directly or
indirectly) of more than fifty percent (50%) of the outstanding voting
securities of a corporation or comparable equity interest in any other type of
entity.

         1.2  "Agreement" means the present agreement together with all exhibits
and schedules.

         1.3  "BI Technology" means all Know-How and Patent Rights to the extent
necessary or appropriate for the full development, use or sale of the Compound
or the Product, now or during the term hereof, (a) owned by BI or one of its
Affiliates, or (b) to the extent BI (or its Affiliate) is permitted to grant a
sublicense to Vion, licensed to BI or one of its Affiliates by a Third Party.
<PAGE>

         1.4  "BI Trademarks" means trademarks for use on the Product (other
than the Vion Trademarks) designated by BI from time to time in accordance with
Section 3.3(a) below.

         1.5 "Commercially reasonable and diligent efforts" means those efforts
consistent with the exercise of prudent scientific and business judgment, as
applied to other products of similar scientific and commercial potential in the
country in which the Product would be marketed and sold.

         1.6 "Compound" means the compound porfiromycin.

         1.7 "Confidential Information" means all information and materials
received by either party from the other party pursuant to this Agreement and all
information and materials developed in the course of the parties' collaboration,
including, without limitation, Know-How of each party, subject to the exceptions
set forth in Section 7.2.

         1.8 "Deductions" means: (a) trade discounts, trade credits or returns,
recalls, chargebacks, rebates and prompt payment discounts, (b) transportation
charges and insurance expenses, (c) Medicare, Medicaid and managed care rebates,
fees or refunds actually granted to health care organizations, governments and
their agencies, purchasers and reimbursers, all of which are granted in the
ordinary course of BI's business, (d) any government imposed fees, other than
income taxes, required to permit manufacture, marketing, or sale of the Product
in the Territory, such fees include, but are not limited to, establishment fees,
submission review fees, and product registration fees, and (e) sales taxes, use
taxes, duties and other similar taxes borne by BI, its Affiliates, Recognized
Agents or permitted sublicensees provided, in each case, to the extent such
items are actually included in the price charged to such Third Parties for the
Product.

         1.9 "Development Plan" means the plan prepared pursuant to this
Agreement by BI for development and commercialization of the Product. A copy of
which Development Plan will be provided to Vion. The Development Plan may be
amended by BI at BI's sole discretion.

         1.10 "Development Work" means the research and development program
performed by BI as described in the Development Plan under BI's direction and
conducted in accordance with the terms and conditions of this Agreement.

         1.11 "Development Work Under The Original Agreement" shall mean the
research and clinical development program performed by the parties in accordance
with the terms and conditions of the Original Agreement.

         1.12 "FDA" means the United States Food and Drug Administration (or its
substantial equivalent in any foreign country).

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         1.13 "FDA Act" means the United States Food, Drug and Cosmetic Act, as
amended.

         1.14 "First Commercial Sale" of the Product shall mean the first sale
for use or consumption of the product in a country after required marketing and
pricing approval has been granted by the governing health regulatory authority
of such country. A sale to an Affiliate, Recognized Agent or permitted
sublicensee shall not constitute a First Commercial Sale.

         1.15 "IND" means Investigational New Drug Application No. 52,804 filed
for the Product with the FDA or its substantial equivalent in any foreign
country.

         1.16 "Invention" means any discovery or invention made by either party
relating to the Compound or Product.

         1.17 "Know-How" means techniques; inventions, practices; methods;
knowledge; know-how; skill; experience; and test data, including, without
limitation, pharmacological, toxicological and clinical test data, analytical
and quality control data.

         1.18 "Major Country" means any of the following: (i) the European
Union, and (ii) the United States.

         1.19 "NDA" means a New Drug Application in the United States (or the
equivalent application in any other country) and all supplements filed pursuant
to the requirements of the FDA, including all documents, data and other
information concerning products which are necessary for or included in NDA
Approval.

         1.20 "NDA Approval" means FDA approval of an NDA.

         1.21 "Net Sales" means the gross amounts invoiced by BI, its Affiliates
or to the extent permitted under Section 3.4, Recognized Agents or permitted
sublicensees of BI or its Affiliates, to Third Parties for sales of the Product
for use in the treatment or prevention of cancer in humans less the Deductions
as determined in accordance with Section 4.3 below. The transfer of the Product
by BI or one of its Affiliates to (i) another Affiliate of BI, (ii) a permitted
sublicensee of BI, or (iii) a Recognized Agent shall not be considered a sale.

         1.22 "North America" shall mean the United States of America and
Canada.

         1.23 "Original Agreement" means the Collaboration Development and
Distribution Agreement between Vion and BI dated November 24, 1997.

         1.24 "Patent Rights" means all rights existing during or after the term
of the Original Agreement or this Agreement under (a) patents (including
inventor's certificates) that include one or more Valid Claims, including
without limitation any substitution, extension, registration, confirmation,
reissue, re-examination, renewal, supplementary protection certificate or the
like and (b) pending applications for patents, including without limitation any
continuation, division or continuation-in-part thereof and any provisional
applications.

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         1.25 "Product" means a pharmaceutical product in an injectable dosage
form, containing the Compound.

         1.26 "Recognized Agent" shall mean an entity other than an Affiliate of
BI through which BI regularly distributes and sells its products in a particular
country or region.

         1.27 "Royalty" shall have the meaning set forth in Section 4.2.

         1.28 "Royalty Term" means, in any country, the period of time equal to
the longer of: (a) if the sale of the Product in such country is covered by a
Valid Claim, the term of such Valid Claim; or (b) seven (7) years from the date
of the First Commercial Sale of the Product in such country, unless modified by
the terms of Article 11.

         1.29 "Territory" shall mean all countries and territories in the world.

         1.30 "Third Party" means any entity other than Vion or BI or an
Affiliate or sublicensee of Vion or BI.

         1.31 "Trademarks" means the Vion Trademarks and the BI Trademarks.

         1.32 "Transition Plan" means the plan developed by BI and Vion to
facilitate the transfer of research and development conducted, managed or
otherwise facilitated by Vion (including, but not limited to activities
conducted by Covance Clinical Research, Ltd., Covance Inc., and/or Pharm-Olam,
Ltd.) under the Original Agreement to BI and as further defined in Article 10.
The Transition Plan is attached hereto as Exhibit A.

         1.33 "Valid Claim" means, to the extent covering the Compound or the
Product, a marketing exclusivity right conferred as a result of: (i) a
designation as a drug for rare diseases or conditions under Section 526 et. al.
of the FDC Act (or the equivalent rights in any country outside the United
States), or (ii) an exclusive right to sell under an NDA pursuant to Section 505
(j) (4) of the FDC Act (or the equivalent rights in any country outside the
United States).

         1.34 "Vion Technology" means all Know-How and Patent Rights to the
extent necessary or appropriate for the full development, use or sale of the
Compound or the Product, which is, during the term of the Original Agreement,
now, or during the term hereof (a) owned by Vion or one of its Affiliates, or
(b) to the extent Vion (or its Affiliate) is permitted to grant a sublicense to
BI, licensed to Vion or one of its Affiliates by a Third Party. Vion Technology
as of the Effective Date includes, but is not limited to, the Know-How and
Patent Rights listed on Schedule 1 attached hereto.

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         1.35 "Vion Trademarks" means Promycin(R) and such other trademarks
owned and/or used by Vion for use in conjunction with the development and
commercialization of Product.

                       ARTICLE 2. RESEARCH AND DEVELOPMENT
                       -----------------------------------

         2.1 Responsibility. BI, consistent with the terms and conditions of
this Agreement, will conduct research and development on the Compound with the
goal of further development of the Compound into Product for commercialization
as more specifically provided in the Development Plan. BI shall have sole
discretion to determine the scope and conduct of research and development of the
Compound and Product. As provided in Section 2.3 below, Vion, consistent with
the Transition Plan, Development Plan, this Agreement, and as otherwise
requested by BI, shall cooperate fully with BI to facilitate development, NDA
submission(s), NDA Approval(s), and maintenance of the NDA(s). Except as
otherwise provided in this Agreement and the attachments hereto, BI shall be
responsible for the preparation of NDA(s), for filing and maintaining NDA(s) and
for all expenses for filing and maintaining NDA(s), which NDA(s) shall be owned
by BI.

         2.2 Research and Development Efforts. BI shall use commercially
reasonable efforts to perform its responsibilities under the Development Plan.
The Development Work shall be conducted in compliance with applicable good
clinical, laboratory, and manufacturing practices and other legal requirements.

         2.3 Availability of Resources.

         (a) Vion shall use its best efforts to facilitate the transition
according to the Transition Plan and this Agreement and support BI's efforts to
secure an NDA and commercialize the Product.

         (b) Vion agrees to make its employees and non-employee consultants, and
all data, records or other information relating to development of the Compound
and/or Product reasonably available at its facilities (or at such other
non-employee consultants' facilities, as necessary) and at its own cost to
consult with BI on issues arising during the transition, the Development Work,
commercialization of the Product, or in connection with any request or request
for inspection from any regulatory agency, including, without limitation,
regulatory, scientific, technical and clinical testing issues. Representatives
of BI may, upon reasonable notice and at times reasonably acceptable to Vion (or
other non-employee consultants): (i) visit the facilities where the Development
Work or Development Work Under The Original Agreement is or has been conducted,
provided, that if such facilities are not under Vion's control, Vion shall use
reasonable efforts and cooperate with BI to permit BI access to such facilities;
(ii) consult informally, during such visits and by telephone, with Vion
personnel that performed or is performing the Development Work or Development
Work Under The Original Agreement, and

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(iii) review the data, records, or other information relating to the development
of the Compound and/or Product.

         2.4 Allocation of Costs.

         (a) All costs that accrue for Development Work Under The Original
Agreement performed prior to May 1, 1999 will be allocated according to the
terms of the Original Agreement. BI shall, subject to Section 4.2(b) below,
reimburse to Vion Vion's share of the costs of development for Development Work
Under The Original Agreement performed between May 1, 1999 and the Effective
Date.

         (b) Notwithstanding Section 2.4(a) above, the parties acknowledge and
agree that Covance fees for Development Work Under The Original Agreement
performed prior to September 27, 1999 is an amount fixed at [] and Covance
non-investigator pass-through fees accrued prior to September 27, 1999 is an
amount fixed at []. BI shall reimburse Vion for [] of these costs.

         (c) Except as expressly provided in the Transition Plan or this
Agreement, or as agreed from time to time by the parties, all costs of
development for Development Work performed after the Effective Date shall be the
sole responsibility of BI. Notwithstanding the foregoing, in no event shall BI
be obligated to pay any late charges, penalties or damages Vion has incurred or
may incur for failure to make any timely payments to its vendors or as the
result of its failure or alleged failure to fulfill any obligations to its
vendors, including penalties for early termination of contracts with vendors
including, but not limited to, []

         (d) The parties acknowledge and agree that, pursuant to the Original
Agreement, Vion is responsible for the manufacture and costs of Compound and
Product necessary to conduct Development Work Under The Original Agreement. BI
agrees to purchase from Vion, at a price equal to the lesser of U.S. [] per gram
or Vion's actual cost, Compound that: (i) was purchased by Vion prior to the
Effective Date, (ii) meets all required technical specifications (which shall be
mutually agreed to by BI and []), iii) has been manufactured according to all
applicable good manufacturing standards (including, but not limited to, United
States cGMP regulations) and in a manner that allows the Compound to be used
without restriction in BI's Development Work pursuant to this Agreement, and
(iv) in amounts reasonably necessary and appropriate, as determined solely by
BI, to perform Development Work pursuant to this Agreement. BI may, in its sole
discretion, analyze Compound or Product described in this Section 2.4(d) to
determine compliance with the specifications. BI shall purchase Compound
pursuant to this Section 2.4(d) on a standard Boehringer Ingelheim
Pharmaceuticals, Inc. purchase order and all the terms and conditions of such
purchase order shall apply unless explicitly modified by this Agreement.

         (e) Preclinical studies performed by Vion will be appropriately audited
at Vion's expense for quality assurance, such audits to be completed prior to
January 1, 2000. Any remediation required for preclinical studies performed by
Vion shall be performed at Vion's sole expense.

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         2.5 Disclosure; Reports. BI will meet annually, or as mutually agreed,
with Vion senior management to provide the status of the Development Work and
commercialization of the Product.

         2.6 Exclusivity. Neither Vion, nor any of its Affiliates, shall during
the term of this Agreement either directly or indirectly, enter into any
agreement, or engage in, either alone or with any sublicensee or Third Party,
any research, development, manufacture, or commercialization of the Compound or
Product.

                    ARTICLE 3. DISTRIBUTION & LICENSE RIGHTS;
                    -----------------------------------------
                            COMMERCIALIZATION EFFORTS
                            -------------------------

         3.1 Grant of Rights. For the duration of this Agreement, Vion grants BI
an exclusive license in the Territory under the Vion Technology to develop, use
and sell Compound and Product, and to manufacture Product from Compound.

         3.2 Commercialization Efforts.

         (a) Subject to Section 3.2(b) and Section 11.2(c) below, BI shall use
commercially reasonable and diligent efforts to commercialize the Product
consistent with the Development Plan. Subject to Section 3.2(b) below, BI shall
have sole discretion to determine the scope and conduct of commercialization
efforts of the Product.

         (b) Within twenty-four (24) months after the date of the first NDA
Approval in a Major Country, or thereafter during the term of this Agreement, BI
shall identify in writing to Vion those countries in the Territory that neither
BI, nor its Affiliates nor its permitted sublicensees plans to market and sell
the Product. Upon receipt of such written notice, Vion may elect to market the
Product in the countries so identified, subject to the royalty obligations of
Section 4.2. Should Vion elect to market the Product pursuant to this Section
3.2, and providing that BI is marketing and selling Product in the Territory,
Vion agrees to purchase Product from BI and BI agrees to sell Product to Vion.
The sale price of Product to Vion under this Section 3.2 shall be equal to []
The parties agree to negotiate in good faith such other terms and conditions
required to supply Product to Vion pursuant to this Section 3.2 (b).

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         3.3 Trademarks.

         (a) Vion hereby grants to BI an exclusive, worldwide royalty-free
license to use the Vion Trademarks in connection with the promotion and sale of
the Product for so long as BI, a BI Affiliate, a Recognized Agent, or
sublicensee is distributing the Product. BI shall have the right to promote and
sell the Product using the Vion Trademarks or any other trademark that, in BI's
sole discretion, BI desires to use in connection with the promotion and sale of
the Product.

         (b) Each party shall own, register and maintain, at its own expense,
its own Trademarks.

         (c) BI acknowledges that it has and will obtain no proprietary interest
in the Vion company name or the Vion logos (collectively, the "Vion Tradenames")
or the Vion Trademarks and agrees that it: (i) will not attempt to register the
Vion Trademarks or Tradenames, or any colorable imitation thereof, or in any way
assist a Third party to do so; (ii) will not use the same as part of its
corporate or business name; (iii) will not make any representation that it owns
any rights in or to the Vion Trademarks or Tradenames, and (iv) will use the
Vion Trademarks and Vion Tradenames as permitted under this Agreement.

         (d) Vion acknowledges that it has and will obtain no proprietary
interest in the BI Trademarks or the BI Tradenames and agrees that it: (i) will
not attempt to register the BI Trademarks or Tradenames, or any colorable
imitation thereof, or in any way assist a Third Party to do so; (ii) will not
use the same as part of its corporate or business name; and (iii) will not make
any representation that it owns any rights in or to the BI Trademarks or
Tradenames.

         (e) Should BI, pursuant to Section 3.3(a) above, choose to use the Vion
Trademarks in connection with the promotion and sale of the Product, BI shall
submit, on written request of Vion, but not more than once per year, to Vion's
Quality Assurance Department for review for trademark purposes, sample packaging
of the Product and advertising materials which bear or show the Vion Trademarks.
BI shall not sell any Product or utilize any advertising or packaging materials
bearing or showing the Vion Trademarks which in any way is inconsistent with
this Agreement.

         3.4 Assignment or Sublicense to Affiliates or Third Parties.

         (a) BI shall have the unrestricted right to assign or sublicense any or
all of its rights or obligations under this Agreement to any of its Affiliates
or to a Third Party; provided, that such assignment shall not relieve BI of its
responsibilities for performance of its obligations under this Agreement.

         (b) BI may also sublicense its rights to sell the Product to Recognized
Agents in the Territory.

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         3.5 Preservation of Licenses in Bankruptcy.

         (a) If Vion should file a petition under bankruptcy laws, or if any
involuntary petition shall be filed against Vion, BI shall be protected in the
continued enjoyment of BI's rights as licensee hereunder to the maximum feasible
extent permitted under the law, including, without limitation, if it so elects,
the protection conferred upon licensees under Section 365(n) of Title 11 of the
United States Code, or any similar provision of any applicable law. Vion shall
give BI reasonable prior notice of the filing of any voluntary petition, and
prompt notice of the filing of any involuntary petition, under any bankruptcy
laws.

         (b) The Vion Technology shall, to the extent permitted under the law,
be deemed to be "intellectual property" as that term is defined in 11 U.S.C.
Section 101 or any successor provision and shall include Patent Rights, if any.

                         ARTICLE 4. PAYMENT OBLIGATIONS
                         ------------------------------

         4.1 Milestone Payments. Upon achievement of each of the following
milestones (in whatever order they occur), BI shall pay to Vion the
nonrefundable milestone payments set forth below:

         (a)   [];

         (b)   []

All such payments shall be made by wire transfer to the bank account designated
by Vion within thirty (30) days after achievement of the applicable milestone.

         4.2 Royalties.

         (a) BI shall pay to Vion a royalty on the Net Sales of the Product in
North America at a royalty rate of [] percent. BI shall pay to Vion a royalty on
the Net Sales of the Product in the remainder of the Territory at a royalty rate
of []. In the event that Vion markets the Product pursuant to Section 3.2(b),
Vion shall pay to BI a Royalty on the Net Sales of the Product in the countries
so identified at a royalty rate of []. Royalty payments shall continue to accrue
and be payable with respect to sales of the Product and will automatically
expire on a country-by-country basis upon the expiration of the Royalty Term in
such country.

         (b) Notwithstanding Section 4.2 (a) above, the parties acknowledge that
BI paid to Vion an initial license fee pursuant to Section 6.1 of the Original
Agreement in the amount of U.S. $4.0 million, which amount Vion was to have used
exclusively for the development of Promycin(R) as defined by the terms of the
Original Agreement. Pursuant to the Transition Plan, Vion shall provide an
accounting of the amount of the initial license fee that has been used for
development of Promycin(R). Any amount of the initial

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license fee that has not been used for development of Promycin(R) ("Remaining
Amount") shall be identified and applied against any costs of development for
which BI has agreed to reimburse Vion pursuant to Section 2.4. Any portion of
the Remaining Amount still remaining thereafter shall be set off by BI against
Royalty payments in installments equal to no more than [] of any applicable
Royalty.

         4.3 Net Sales and Deemed Deductions. For twelve (12) months following
the First Commercial Sale (hereinafter, the "First Annual Period", each twelve
(12) month period thereafter, an "Annual Period") in order to facilitate BI's
data collection and payment of Royalties, Deductions for the First Annual Period
shall be deemed to be equal to ten percent (10%) of the gross invoice amount of
Product sold to Third Parties for use in the treatment or prevention of cancer
in humans (the "Deemed Amount"); provided, however, that: (a) within sixty (60)
days following the end of the First Annual Period and each Annual Period
thereafter, BI shall provide Vion with all necessary information (in sufficient
detail) to permit Vion to confirm whether the Deemed Amount accurately reflects
the actual Deductions for the applicable Annual Period, and (b) within sixty
(60) days thereafter, the parties shall: (i) determine the actual Deductions
pertaining to the sale or other disposition of the Product for the applicable
Annual Period; (ii) if the Deemed Amount is determined to be greater than or
less than the actual Deductions by more than five percent (5%) or $50,000,
whichever is larger, make prompt retroactive adjustments to the Royalty payments
made during such Annual Period on the basis of the Deemed Amount; and (iii)
determine, in good faith, any appropriate adjustments to the Deemed Amount for
the following Annual Period, or if the parties are unable to agree on a Deemed
Amount, agree that actual Deductions shall be used to determine Net Sales
thereafter.

                       ARTICLE 5. PAYMENT; RECORDS, AUDITS
                       -----------------------------------

         5.1 Payment; Reports. All Royalty payments due under this Agreement
shall be paid within sixty (60) days of the end of each calendar quarter, unless
otherwise specifically provided herein. Each payment of Royalties shall be
accompanied by a report of Net Sales of the Product on a country-by-country
basis in the Territory in sufficient detail to permit confirmation of the
accuracy of the Royalty payment made.

         5.2 Exchange Rate; Manner and Place of Payment. Royalty payments and
reports due pursuant to this Agreement shall be calculated and reported for each
calendar quarter. Exchange conversion of foreign payments into U.S. Dollars
shall be made as necessary at the rate of exchange reported by the Deutsche
Bank, Frankfurt am Main, Germany on the date payment is made. All payments owed
under this Agreement shall be made by wire transfer, unless otherwise specified
by the payee.

         5.3 Records and Audit. During the term of this Agreement and for a
period of two (2) years thereafter, the parties shall each keep complete and
accurate records pertaining to the development of the Compound and sale or other
disposition of the Product in sufficient detail to permit the other party to
confirm the accuracy of all

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payments due hereunder. Each party shall have the right to cause an independent,
certified public accountant to audit such records to confirm Net Sales and
Royalty for the preceding year. Such audits may be exercised on a mutually
agreed date and during normal business hours once a year. The party requesting
the audit shall bear the full cost of such audit unless such audit discloses a
variance of more than five percent (5%) or $50,000 (whichever is larger) from
the amount of the Net Sales, Royalties or other payments due under this
Agreement. In such case, the audited party shall bear the actual out-of-pocket
cost of such audit. The terms of this Section 5.3 shall survive any termination
or expiration of this Agreement for a period of two years.

         5.4 Withholding Obligations.

         (a) Subject to Section 5.4(b), BI and Vion (to the extent Vion pays
Royalties pursuant to Sections 3.2(b) and 4.2(a)) shall be entitled to deduct
any required withholding taxes and other statutory duties from the Royalties and
milestone payments to be made pursuant to Sections 4.1 hereof, and pay such
taxes and duties to the proper tax authorities as required by law applicable at
the time of payment.

         (b) The parties shall exercise reasonable efforts to insure that any
withholding taxes are reduced to the extent possible under the provisions of the
current or any future double taxation agreement between the United States of
America and the Federal Republic of Germany, under which current law requires a
certificate of tax exemption from the German Bundesamt fuer Finanzen.

         (c) In order to achieve the applicable reduction in withholding, Vion
will provide BI with the application for a certificate of tax exemption for
royalties under the United States - Germany Double Taxation Treaty, on the
official form (Application for Tax Exemption) and signed by Vion. The
Certificate for Filing a tax return (IRS Form 6166) shall be enclosed with the
Application for Tax Exemption. BI will provide Vion with the official forms and
Vion will promptly complete them after the Effective Date.

         (d) Every three (3) years, or on such other schedule as the parties may
agree, Vion will submit a new Application for Tax Exemption that complies with
the requirements set forth in Section 5.4(c) above.

            ARTICLE 6. INTELLECTUAL PROPERTY RIGHTS AND INFRINGEMENT.
            ---------------------------------------------------------

         6.1 Patentable Inventions. BI shall own all Inventions made solely by
its employees and agents, and all Patent Rights claiming such Inventions. Vion
shall own all Inventions made solely by its employees and agents, and all Patent
Rights claiming such Inventions.

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         6.2 Infringement by Third Parties.

         (a) BI and Vion shall promptly notify each other in writing of any
alleged or threatened infringement of the Trademarks or the BI or Vion
Technology of which they become aware. Both parties shall cooperate with each
other in the defense or prosecution of infringement matters, including if
required to bring such action, the furnishing of a power of attorney.

         (b) Vion shall have the first right to bring and control any action or
proceeding with respect to any alleged or threatened infringement of the Vion
Trademarks or the Vion Technology at its own expense and by counsel of its own
choice, and BI shall have the right, at its own expense, to be represented in
any such action by counsel of its own choice. BI shall have the first right to
bring and control any action or proceeding with respect to any alleged or
threatened infringement of the BI Trademarks or BI Technology at its own expense
and by counsel of its own choice, and Vion shall have the right, at its own
expense, to be represented in any such action by counsel of its own choice.

         (c) If either party with the first right as provided herein fails to
bring an action or proceeding within (i) ninety (90) days following the notice
of alleged infringement or (ii) ten (10) days before the time limit, if any, set
forth in the appropriate laws and regulations for the filing of such actions,
whichever comes first, the other party shall have the right to bring and control
any such action at its own expense and by counsel of its own choice, and the
party with the first right shall have the right, at its own expense, to be
represented in any such action by counsel of its own choice; provided, however,
that Vion shall not have the right to bring or control any such action with
respect to the alleged infringement of a BI Trademark.

         (d) In the event that the party with the second right elects to bring
an action as provided in Section 6.2(c), such party shall be entitled to: (i)
reimbursement of fifty percent (50%) of its costs and expenses, or (ii) offset
fifty percent (50%) of its costs and expenses against Royalties due hereunder
(in the event that BI brings such action), but in no event shall the Royalty to
Vion be reduced by more than fifty percent (50%) of the amount due in any given
calendar quarter; provided, however, that in the event that the party with the
second right elects to bring an action as provided in Section 6.2(c) with
respect to any alleged or threatened infringement of any of the Trademarks, such
party shall be entitled to reimbursement of all of its costs and expenses.

         (e) Neither party shall have the right to settle any infringement
litigation under this Section 6.2 in a manner that diminishes the rights or
interests of the other party without the consent of such other party. Except as
otherwise agreed to by the parties as part of a cost sharing arrangement, any
recovery realized as a result of such litigation, after reimbursement of any
litigation expenses of BI and Vion (including, any offset Royalties) shall
belong to the party who brought the action.

                                       12
<PAGE>

         6.3 Infringement of Third Party Rights.

         (a) BI and Vion shall promptly notify each other in writing of any
allegation or claim by a Third Party that the manufacturing, marketing or sale
of the Product infringes or may infringe the intellectual property rights of
such Third Party.

         (b) Vion shall have the obligation to control any defense of such claim
if it relates to Vion Technology or the Vion Trademarks, and BI shall have the
obligation to control any defense of such claim if it relates to BI Technology
or the BI Trademarks, in each case, at its own expense. In each case, the party
not controlling the defense shall have the right, at its own expense, to be
represented in any such action by counsel of its own choice.

         (c) Neither party shall have the right to settle any infringement
litigation under this Section 6.3 in a manner that diminishes the rights or
interests of the other party without the consent of such other party.

                           ARTICLE 7. CONFIDENTIALITY
                           --------------------------

         7.1 Nondisclosure. During the term of this Agreement and for a period
of ten (10) years after termination hereof, each party will maintain all
Confidential Information in trust and confidence and will not disclose any
Confidential Information to any Third Party or use any Confidential Information
for any purpose except as expressly authorized by this Agreement, including
Section 7.3. Each party may use such Confidential Information only to the extent
required to accomplish the purposes of this Agreement. Each party will use at
least the same standard of care as it uses to protect proprietary or
confidential information of its own to ensure that its employees, agents,
consultants and other representatives do not disclose or make any unauthorized
use of the Confidential Information. Each party will promptly notify the other
upon discovery of any unauthorized use of disclosure of the Confidential
Information.

         7.2 Exceptions. Confidential Information shall not include any
information that the receiving party can prove by competent evidence:

         (a) Is now, or hereafter becomes, through no act or failure to act on
the part of the receiving party, generally known or available;

         (b) Is known by the receiving party at the time of receiving such
information, as evidenced by its records;

         (c) Is hereafter furnished to the receiving party by a Third Party, as
a matter of right and without restriction on disclosure;

         (d) Is independently developed by the receiving party without the aid,
application or use of Confidential Information; or

                                       13
<PAGE>

         (e) Is the subject of a written permission to disclose provided by the
disclosing party;

         7.3 Financial Terms. Except as required by applicable law (including,
but not limited to securities laws), the parties agree that the material
financial terms of this Agreement will be considered Confidential Information of
both parties. Notwithstanding the foregoing, either party may disclose such
terms as are required to be disclosed in its financial statements. Either party
shall have the further right to disclose the material financial terms of this
Agreement under strictures of confidentiality to any potential acquiror, merger
partner or other bona fide potential strategic partner.

              ARTICLE 8. REPRESENTATIONS, WARRANTIES AND COVENANTS
              ----------------------------------------------------

         8.1 Corporate Power. Each party represents and warrants to the other
that: (a) it has the legal right and power to enter into this Agreement and to
extend the rights and licenses granted to the other herein; and (b) the
performance of such obligations will not conflict with its charter documents or
any agreements, contracts or other arrangements to which it is a party.

         8.2 Organization; Due Authorization. BI represents and warrants to Vion
that BI is a limited liability company duly organized, validly existing and in
good standing under applicable German law and has taken all necessary action to
authorize the execution, delivery and performance of this Agreement. Vion
warrants to BI that Vion is a corporation duly organized, validly existing and
in good standing under applicable Delaware law and has taken all necessary
action to authorize the execution, delivery and performance of this Agreement.

         8.3 Binding Agreement. Each party represents and warrants to the other
that, upon the delivery and execution of this Agreement, this Agreement shall
constitute a valid and binding obligation of such party enforceable in
accordance with its terms, except as enforceability may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium or similar laws affecting
creditors' rights generally and except as enforceability may be subject to
general principles of equity (regardless of whether such enforceability is
considered in a proceeding in equity or at law).

         8.4 Intellectual Property Rights. Vion represents and warrants that, as
of the Effective Date, to the best of its knowledge and belief: (a) there are no
unexpired patents claiming the Compound, its uses or methods for its
manufacture; (b) the manufacture, sale and use of the Product as contemplated in
this Agreement, does not infringe the patent rights of any Third Parties; (c)
Vion owns or possesses and shall maintain adequate licenses or other rights to
all Patents and Know-How necessary to grant the licenses granted to BI under
Article 3 hereof and fulfill its other obligations hereunder. Vion further
represents and warrants that, to the best of its knowledge and belief, there are
not now any threatened or pending proceedings against Vion by any Third Party
that would interfere with or prevent BI from using the Vion Technology, the
Compound, its uses or

                                       14
<PAGE>

methods for manufacture or the Vion Trademarks as provided herein; and (d) none
of the research on the Compound conducted in Dr. Alan Sartorelli's laboratory
was funded by the United States Government. Vion further represents and warrants
to BI that Vion has no Patent Rights, proprietary interest in, or ownership of
any technology in any way relating to manufacture of the Compound or Product.
Vion further represents and warrants that BI by manufacture of the Compound
shall not infringe any proprietary right owned by Vion.

         8.5 Compliance with Laws. Each party hereby represents, warrants,
covenants and agrees that it shall comply with all applicable foreign, federal,
state and local laws and regulations relating to the manufacture, use,
distribution and sale of the Product by such party as contemplated by this
Agreement. Vion further represents, warrants, covenants and agrees that it
complied with all applicable foreign, federal, state and local laws and
regulations in performing Development Work Under The Original Agreement.

         8.6 Data and Information. Vion represents and warrants that, as of the
Effective Date, to the best of its knowledge and belief, all data and
information provided by Vion to BI hereunder concerning the Vion Technology and
the Compound and Product are true and correct in all material respects.

         8.7 Disclaimer of Warranties. The parties understand that the
Collaboration will involve technologies that have not been approved by any
regulatory authority and that neither party guarantees the safety or usefulness
of the Compound of the Product. EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT,
NEITHER PARTY MAKES ANY REPRESENTATION OR WARRANTY TO THE OTHER PARTY OF ANY
NATURE, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTY OF
NONINFRINGEMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

         8.8 Cooperation. Vion represents and warrants to BI that it will use
its best efforts to transition all its responsibilities under the Original
Agreement that have been transferred to BI pursuant to this Agreement. Vion
further represents and warrants that to the best of its knowledge and belief it
has provided to BI all relevant information and documentation in its possession
pertaining to the Development Work Under The Original Agreement and has given BI
written notification of all matters pertaining to the Development Work Under The
Original Agreement including, but not limited to, all communications (written or
oral) and/or contracts with investigators, FDA, contract research organizations,
vendors or other Third Parties. Vion further represents and warrants that to the
extent clinical, regulatory, or other information which is in Vion's possession
or control is lacking or later required, Vion will promptly notify BI of such
fact and/or promptly provide such information to BI.

                                       15
<PAGE>

                              ARTICLE 9. INDEMNITY
                              --------------------

         9.1 Vion Indemnity Obligations. Vion shall indemnify, defend and hold
BI and its Affiliates and their respective employees and agents harmless from
and against any and all claims, liability, damage, loss, cost or expense,
including without limitation reasonable legal fees, in connection with any Third
Party claims which (a) arise out of any breach of any material provision of this
Agreement or any representation or warranty of Vion contained in this Agreement,
or (b) arise out of any claim of infringement of any patent or trademark or
unauthorized use of a trade secret (other than the BI Trademarks or the BI
Technology) in connection with the use of the Vion Technology or Vion Trademarks
as contemplated by this Agreement, (c) arise out of any third party actions
arising out of Vion's activities under the Original Agreement, including but not
limited to, actions arising out of Vion's contracts with Sicor S.p.A., Vinchem,
Inc., Alco Chemicals Ltd., Covance Clinical Research Unit, Ltd., Covance Inc.

         9.2 BI Indemnity Obligations. BI shall indemnify, defend and hold Vion,
its Affiliates and their respective employees and agents harmless from the
against any and all claims, liability, damage, loss, cost or expense, including
without limitation reasonable legal fees, in connection with any Third Party
claims which: (a) arise out of any breach of any material provision of this
Agreement or any representation or warranty of BI contained in this Agreement,
or (b) arise out of any claim of infringement of any patent or trademark or
unauthorized use of a trade secret (other than the Vion Trademarks or the Vion
Technology) in connection with the use of the BI Technology or BI Trademarks as
contemplated by this Agreement, or (c) arise out of claims for bodily injury,
death or property damage arising from the distribution, use or sale of the
Product hereunder or manufacture or labeling of the Product when manufactured or
labeled by BI or a BI Affiliate or a BI sublicensee, to the extent attributable
to any failure by BI, its Affiliates or sublicensees to perform their
obligations hereunder in accordance with applicable laws and regulations
(except, in each case, to the extent such claim relates to the negligence or
willful misconduct of Vion).

         9.3 Procedure. A party or any of its Affiliates or their respective
employees or agents (the "Indemnitee") that intends to claim indemnification
under this Article 9 shall promptly notify the other party (the "Indenmitor") of
any loss, claim, damage, liability or action in respect of which the Indemnitee
intends to claim such indemnification, and the Indemnitor shall assume the
defense thereof with counsel mutually satisfactory to the parties; provided,
however, that the Indemnitee shall have the right to retain its own counsel,
with the fees and expenses to be paid by the Indemnitor, if representation of
such Indemnitee by the counsel retained by the Indemnitor would be inappropriate
due to actual or potential differing interests between such Indemnitee and any
other party represented by such counsel in such proceedings. The indemnity
agreement in this Article 9 shall not apply to amounts paid in settlement of any
loss, claim, damage, liability or action if such settlement is effected without
the consent of the Indemnitor, which consent shall not be withheld unreasonably.
The failure to deliver notice to the Indemnitor within a reasonable time after
the commencement of any such action, if prejudicial to its ability to defend
such action, shall relieve such Indemnitor of any

                                       16
<PAGE>

liability to the Indemnitee under this Article 9, but the omission so to deliver
notice to the Indemnitor will not relieve it of any liability that it may have
to any Indemnitee otherwise than under this Article 9. The Indemnitee under this
Article 9, its employees and agents, shall cooperate fully with the Indemnitor
and its legal representatives in the investigation of any action, claim or
liability covered by this indemnification.

         9.4 Insurance. BI and Vion shall each maintain appropriate product
liability insurance with respect to the development, manufacture and sales of
the product by BI and Vion, respectively, in such amount as BI and Vion,
respectively, customarily maintain with respect to the manufacture or sales of
its other products.

                             ARTICLE 10. TRANSITION
                             ----------------------

         10.1 Transition Plan. The parties acknowledge and agree that to meet
the goals of this Agreement, a successful, efficient and complete transition of
Vion's Development Work Under The Original Agreement to BI (including all
Development Work Under The Original Agreement actually performed by Vion as well
as work performed by Third Parties managed by Vion) is required. As such, Vion
agrees to fully meet its obligations under the Transition Plan, a copy of which
is attached hereto and made a part hereof. The Transition Plan shall, at a
minimum, require: i) a financial accounting of all the costs of Development Work
Under The Original Agreement up to the Effective Date, ii) a list of all vendors
or other Third Parties engaged directly or indirectly by Vion that have assisted
or performed Development Work Under The Original Agreement, iii) that BI receive
a copy of all contracts entered into by Vion relating to the Vion Technology,
the Compound or the Product, including, but not limited to, all contracts with
Vendors identified pursuant to this Section 10.1(ii) above, iv) a copy of all
purchase orders relating to Development Work Under The Original Agreement
outstanding as of Effective Date, and v) a formal acknowledgment by Vion that it
has met all the terms and requirements of the Transition Plan and this Article
10.

         10.2 Pre-transition Audits and Remediation.

         (a) Each party acknowledges that this Agreement is contingent upon the
successful completion and satisfactory results (as determined solely by BI) of
audits and assessments of Vion's Development Work Under The Original Agreement
including, but not limited to, audits or assessments of Sicor S.p.A.

         (b) Each party acknowledges transfer of responsibility and ownership of
INDs to BI is contingent upon: i) the successful completion of transfer of Study
PORF-96-001 from Covance to BI, ii) BI's completion of clean up and entry of all
data for all patients recruited into Study PORF-96-001 prior to October 31,
1999, iii) BI's completion of a safety assessment based on the transferred and
updated SAE database of Study PORF-96-001 from Covance, and iv) FDA confirmation
of the acceptability of study PORF-96-001.

                                       17
<PAGE>

         10.3 INDs. Vion agrees that, upon satisfaction of the conditions in
Section 10.2 above and upon BI's request, it will execute or cause to be
executed all documentation required to transfer full and exclusive control and
ownership of the INDs to BI.

         10.4 Joint Technology. BI and Vion each acknowledge that no Joint
Technology, as defined by Section 1.21 of the Original Agreement, exists as of
the Effective Date of this Agreement.

         10.5 Original Agreement. BI and Vion each acknowledge and agree that
except to the extent expressly and explicitly modified by this Agreement, all
terms, conditions, obligations, and rights of each party under the Original
Agreement remain in full force and effect until the Effective Date. Upon the
Effective Date, the Original Agreement will terminate.

                        ARTICLE 11. TERM AND TERMINATION
                        --------------------------------

         11.1 Term. Unless terminated earlier pursuant to Section 11.2, this
Agreement shall expire and the licenses granted by Vion to BI pursuant to
Sections 3.1 and 3.3 (subject to the terms and conditions set forth therein)
shall become fully-paid, on a country by country basis, upon the expiration of
the Royalty Term in such country.

         11.2 Early Termination. Either party may terminate this Agreement upon
the occurrence of any of the following:

         (a) upon or after the bankruptcy, insolvency, dissolution or winding up
of the other party (other than dissolution or winding up for the purposes of
reconstruction or amalgamation);

         (b) upon the material breach of any material provision of this
Agreement by either party (a "Material Breach"), which has not been cured within
sixty (60) days after written notice from the other party (a "Default"). The
non-Defaulting party may, in its discretion, terminate this Agreement
immediately upon written notice of such Default and proceed against the other
party for all applicable damages. Without limiting the generality of the
foregoing, the parties hereto expressly agree that in the event of a Default by
either of them, in addition to all other remedies available at law or in equity,
which may be available to the other, it is agreed that the non-Defaulting party
may, at its option, notify the Defaulting party that it wishes to proceed with
the development of the product on an exclusive basis. []

         []

         (c) Notwithstanding the foregoing, or the provision of Section 3.4, BI
shall have the right in it's sole discretion, upon thirty (30) days prior
written notice, to cease development, manufacture, or sale of Compound or
Product. If BI exercises its rights

                                       18
<PAGE>

under this Section while the product is still in development, BI will phase out
and terminate the development program as it deems appropriate. Upon expiry of
the thirty (30) day period each party hereto shall have no further obligations
to the other, except as set forth Section 11.3 below.

         11.3 Effect of Expiration or Termination.

         (a) Expiration or termination of this Agreement, for whatever reason,
shall not affect any rights or obligations accrued by either party prior to the
effective date of expiration or termination, including without limitation, the
obligation to pay Royalties on Product sold prior to expiration or termination.

         (b) Termination of this Agreement under Section 11.2 shall not
prejudice any claim for damages a party may have under this Agreement.

         (c) Except as otherwise provided in Article 11, upon expiration or
termination of this Agreement both parties shall immediately cease using the
other party's BI or Vion Technology and Confidential Information.

         (d) Termination of this Agreement pursuant to Section 11.2(c) shall
cause the Royalty Term to expire concurrently with the date of termination.

         (e) The obligations and rights of the parties under Articles 7, 9, and
12, and Sections 5.3, 8.4, 11.1 and 11.3 shall survive termination or expiration
of this Agreement.

                            ARTICLE 12. MISCELLANEOUS
                            -------------------------

         12.1 Assignment.

         (a) Notwithstanding any provision of this Agreement to the contrary,
either party may assign any of its rights or obligations under this Agreement:
(i) in any country to any Affiliates; provided, however, that such assignment
shall not relieve the assigning party of its responsibilities for performance of
its obligations under this Agreement; or (ii) in connection with the sale of all
or substantially all of its assets.

         (b) This Agreement shall survive any merger of either party with or
into another party and no consent for a merger or similar reorganization shall
be required hereunder; provided, that in the event of such merger or in the
event of a sale of all assets, no intellectual property rights of the acquiring
corporation shall be included in the technology licensed hereunder.

         (c) This Agreement shall be binding upon and inure to the benefit of
the successors and permitted assigns of the parties. Any assignment not in
accordance with this Agreement shall be void.

                                       19
<PAGE>

         12.2 Publicity.

         (a) Vion shall not, without the prior review and written consent of BI,
publish in any form or in any media any information relating to the Compound or
Product or this Agreement.

         (b) Each party agrees not to publicize or otherwise use the other
party's name except upon the express written consent of such other party.

         12.3 Headings. The descriptive headings in this Agreement are included
for convenience of reference only and shall not affect the meaning or
interpretation of this Agreement.

         12.4 Force Majeure. Neither party shall lose any rights hereunder or be
liable to the other party for damages or losses on account of failure of
performance by the defaulting party if the failure is occasioned by government
action, war, fire, explosion, flood, strike, lockout, embargo, act of God, or
any other similar cause beyond the control of the defaulting party, provided
that the party claiming force majeure has exerted all reasonable efforts to
avoid or remedy such force majeure.

         12.5 Payment in U.S. Dollars. All payments due to either party under
this Agreement shall be paid in U.S. Dollars.

         12.6 Notices. Any notices or communications provided for in this
Agreement to be made by either of the parties to the other shall be in writing,
in English, and shall be made by prepaid air mail with return receipt or by
overnight or similar courier service, addressed to the other at its address set
forth below. Any such notice of communication may also be given by hand, or
facsimile to the appropriate designation. Notices shall be sent:

If to BI, to:              Boehringer Ingelheim International GmbH
                           Postbox 200
                           D-55216 Ingelheim, Rhein
                           Germany
                           Attention: Corporate Licensing
                           Telephone:  011 49 61 32 77 50 63
                           Facsimile:  011 49 61 32 77 42 25

         With a copy to:

                           Boehringer Ingelheim International GmbH
                           Postbox 200
                           D-55216 Ingelheim, Rhein
                           Germany
                           Attention: Head of Legal Department
                           Telephone:  011 49 61 32 77 2106
                           Facsimile:  011 49 61 32 77 3583

                                       20
<PAGE>

If to Vion, to:            Vion Pharmaceuticals, Inc.
                           Four Science Park
                           New Haven, Connecticut 06511
                           Attention:  President and CEO
                           Telephone:  1 203 498 4210
                           Facsimile:  1 203 498 4211

         With a copy to:

                           Terence Jones, Esq.
                           Wiggin & Dana
                           One Century Tower
                           P.O. Box 1832
                           New Haven, Connecticut 06508-1832
                           Telephone:  1 203 498 4324
                           Facsimile:  1 203 782 2889

                                       21
<PAGE>

Either party may, by like notice, specify or change an address to which notices
and communications shall thereafter be sent. Notices sent by mail, facsimile or
cable shall be effective upon receipt and notices given by hand shall be
effective when delivered.

         12.7 Governing Law. This Agreement shall be governed by the laws of the
State of Connecticut, as such laws are applied to contracts entered into and to
be performed within such state without giving effect to conflicts of laws
principles.

         12.8 Waiver. Except as specifically provided for herein, the waiver
from time to time by either of the parties of any of their rights or their
failure to exercise any remedy shall not operate or be construed as a continuing
waiver of same or of any other of such party's rights or remedies provided in
this Agreement.

         12.9 Severability. If any term, covenant or condition of this Agreement
or the application thereof to any party or circumstance shall, to any extent, be
held to be invalid or unenforceable, then (a) the remainder of this Agreement,
or the application of such term, covenant or condition to parties or
circumstances other than those as to which it is held invalid or unenforceable,
shall not be affected thereby and each term, covenant or condition of this
Agreement shall be valid and be enforced to the fullest extent permitted by law;
and (b) the parties hereto covenant and agree to renegotiate any such term,
covenant or application thereof in good faith in order to provide a reasonably
acceptable alternative to the term, covenant or condition of this Agreement or
the application thereof that is invalid or unenforceable, it being the intent of
the parties that the basic purposes of this Agreement are to be effectuated.

         12.10 Independent Contractors. It is expressly agreed that Vion and BI
shall be independent contractors and that the relationship between the two
parties shall not constitute a partnership or agency of any kind. Neither Vion
nor BI shall have the authority to make any statements, representations or
commitments of any kind or to take any action, which shall be binding on the
other, without the prior written authorization of the party to do so.

         12.11 Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         12.12 Entire Agreement. This Agreement sets forth all of the covenants,
promises, agreements, warranties, representations, conditions and understandings
between the parties hereto and supersede and terminate all prior agreements and
understanding between the parties. There are no covenants, promises, agreements,
warranties, representations, conditions or understandings, either oral or
written, between the parties other than as set forth herein and therein. No
subsequent alteration, amendment, change, agreement or addition to this
Agreement shall be binding upon the parties hereto unless reduced to writing and
signed by the respective authorized officers of the parties.

                                       22
<PAGE>

         IN WITNESS WHEREOF, the parties have executed this Agreement in
duplicate originals by their proper officers as of the date and year first above
written.

BOEHRINGER INGELHEIM                     VION PHARMACEUTICALS, INC.
INERNATIONAL GmbH

By:     /s/ Barner                       By:  /s/ Alan Kessman

Name:   Barner                           Name:  Alan Kessman

Title:                                   Title:  President

By:     /s/ Muller                       By:  /s/ Thomas Mizelle

Name:   Muller                           Name:  T. Mizelle

Title:  Authorized Signatory             Title:  VP Operations

                                       23EXHIBIT 10.33
                                                                   -------------

                    CONFIDENTIAL TREATMENT HAS BEEN REQUESTED
                     WITH REGARD TO PORTIONS OF THIS EXHIBIT

                   AMENDMENT TO CLINICAL DEVELOPMENT AGREEMENT

      This Amendment is entered into this 27th day of October, 1999 by and
between Vion Pharmaceuticals, Inc., Four Science Park, New Haven, Connecticut
("Vion"), Covance Clinical Research Unit Ltd., Hyde Street, Leeds, United
Kingdom ("Covance"), and Covance Inc., 210 Carnegie Center, Princeton, New
Jersey ("Covance"), and amends the Clinical Development Agreement between Vion
and Covance dated June 6, 1997 ("Original Agreement").

      WHEREAS, the parties to the Original Agreement desire to effect an
amicable and efficient transfer of Covance's responsibilities (except as
provided hereinafter in Section 2(b)) and terminate the Original Agreement.

      NOW THEREFORE, in consideration of the premises and the undertakings of
the parties hereinafter set forth, the parties agree as follows:

1.    DEFINITIONS

      a.     "Affiliate" means an individual, trust, business trust, joint
             venture, partnership, corporation, limited liability company,
             association or any other entity which owns, is owned by or is under
             common ownership with a party. For the purposes of this definition,
             the term "owns" (including, with correlative meanings, the terms
             "owned by" and "under common ownership with") as used with respect
             to any party, shall mean the possession (directly or indirectly) of
             more than fifty percent (50%) of the outstanding voting securities
             of a corporation or comparable equity interest in any other type of
             entity.

      b.     "FDA" means the United States Food and Drug Administration (or its
             substantial equivalent in any foreign country).

      c.     "IND" means Investigational New Drug Application No. 52,804 filed
             for the Drug with the FDA or its substantial equivalent in any
             foreign country.

      d.     All capitalized terms used herein and not otherwise defined, shall
             have the meaning ascribed thereto under the Original Agreement.

      e.     "BIPI" means Boehringer Ingelheim Pharmaceuticals, Inc.

                                   Page 1 of 5
<PAGE>

2.    OBLIGATIONS OF COVANCE

      a.     Covance shall use its best efforts to cooperate with Vion and BIPI
             to transition its responsibilities under the Original Agreement
             according to the Transition Plan, which is attached as Appendix 1
             to this Amendment (and which may be amended from time to time
             during the transition period). For the purposes of this amendment,
             "best efforts" shall be those efforts Covance would apply to a
             similar project for its most important clients in good standing.
             BIPI and Vion agree that they shall accept such responsibilities in
             accordance with the Transition Plan no later than November 30,
             1999.

      b.     Covance shall continue to perform IVRS patient randomization and
             assignment and clinical trial supply management according to the
             methodology and fee structure as under the Original Agreement and
             in accordance with the Roles and Responsibilities for Protocol No.
             PORF-96-001 dated January 15, 1999 and approved January 18, 1999.
             The fee to Covance for IVRS patient randomization and assignment
             and clinical trial supply management shall be []. The parties agree
             that fees described in this Section 2(b) apply to the first []
             patients randomized and assigned. Covance agrees to perform further
             IVRS randomization and assignment and clinical trial supply
             management at BIPI's request on a PRO RATA cost basis.

      c.     Covance will continue to be responsible for site management of each
             individual research site in accordance with the methodology
             described in the Original Agreement and Transition Plan until BIPI
             (or a BIPI Affiliate) is prepared to take over responsibility for
             such tasks but in no event later than November 30, 1999. It is
             understood and agreed that during the transition herein described,
             these tasks may be performed jointly by Covance and BIPI (or a BIPI
             Affiliate). All agreements with Investigators shall be assigned by
             Covance and accepted by BIPI (or a BIPI Affiliate) no later than
             such date pursuant to a written acknowledgment of such assignment
             and acceptance from each individual research site at which point
             Covance's responsibility for such tasks shall cease. After BIPI (or
             a BIPI Affiliate) has executed a contract with an individual
             research site, Covance shall continue to be responsible for
             reporting all (including Pharm-Olam generated) expeditable and/or
             severe adverse events to the FDA (or other relevant agencies) until
             the date upon which BIPI provides written notice to Covance that
             acceptable data bases have been established at BIPI and all
             relevant BIPI Affiliates, but in no event shall Covance be so
             responsible beyond November 30, 1999.

      d.     BIPI and Covance shall enter a contract for performance of the
             activities described in Section 2(b).

                                   Page 2 of 5
<PAGE>

3.    OBLIGATIONS OF VION

      a.     For all activities performed by Covance and not yet paid by Vion
             through September 27, 1999, Vion shall pay Covance a total of [].
             This payment shall be in full settlement of all amounts owed to
             Covance by Vion for Covance activities under the Original Agreement
             through September 27, 1999 and shall be paid to Covance no later
             than November 30, 1999.

      b.     Vion shall reimburse Covance for pass-through Investigator fees
             that have been incurred by Covance through September 27, 1999 but
             not yet reimbursed by Vion. The amount of the pass-through
             Investigator fees incurred through September 27, 1999 is
             approximately []. For all other outstanding pass-through fees
             incurred by Covance through September 27, 1999, Vion shall
             reimburse Covance a total of []. The sums described herein shall be
             paid no later than November 30, 1999.

      c.     For all fees and pass-through costs other than Investigator fees
             after September 27, 1999, including the transition activities
             described in Section 2(a) above and the Transition Plan, Vion shall
             pay Covance a fee of [], such fee payable within fifteen (15) days
             of the date upon which BIPI provides written notice to Covance that
             acceptable data bases have been established at BIPI and all
             relevant BIPI Affiliates, but in no event later than December 15,
             1999. Vion shall continue to reimburse Covance for pass-through
             Investigator fees incurred by Covance within thirty (30) days of
             invoice.

4.    ORIGINAL AGREEMENT

      a.     Upon the date of formal transfer of responsibility for all INDs
             from Vion to BIPI as defined in Section 5 below, the Original
             Agreement will terminate.

      b.     The confidentiality obligations contained in Section 5, the
             indemnification provisions of Sections 2(l) and 3(h) of the
             Original Agreement shall survive termination of the Original
             Agreement. In addition, the parties agree that the obligation to
             comply with all applicable regulations shall also survive
             termination of the Original Agreement.

                                   Page 3 of 5
<PAGE>

5.    RELEASE FROM LIABILITY

      a.     Upon full review of all the data and information relating to
             Covance's work under the Original Agreement and formal transfer of
             responsibility for all INDs from Vion to BIPI, Vion and Covance
             shall execute a mutual release, from further responsibility or
             liability under the Original Agreement (including a waiver of any
             early termination penalties described in Section 8 of the Original
             Agreement). Such release shall not release Vion or Covance from the
             claims of third parties pursuant to Sections 2(l) and 3(h) of the
             Original Agreement. For the purposes of this Amendment, "formal
             transfer of responsibility" is defined, on a country-by-country
             basis, as notification from BIPI (or a BIPI Affiliate) to the FDA
             of the transfer of sponsor responsibility for the IND from Vion to
             BIPI (or a BIPI Affiliate). The review described herein shall be
             completed by BIPI and Vion no later than March 31, 2000. In the
             event of any complaints with respect to the data and information so
             reviewed, BIPI and Vion shall provide Covance with prompt written
             notice of the same and Covance shall be given an opportunity, if
             practicable, to cure any identified deficiency. In the event of a
             dispute among the parties with respect to this review, the parties
             agree to submit the dispute to non-binding mediation in the event
             that executive discussion cannot resolve the issue to everyone's
             satisfaction.

                                   Page 4 of 5
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed by their duly authorized representatives as of the date and year first
written above.

VION PHARMACEUTICALS, INC.                   COVANCE CLINICAL
                                             RESEARCH UNIT LTD.

By:   /s/ Thomas Mizelle                     By:   /s/ Charles C. Harwood, Jr.
      ---------------------------                  ---------------------------

Its:  VP Operations                          Its:  Director
      ---------------------------                  ---------------------------

Date: October 27, 1999                       Date: October 28, 1999
      ---------------------------                  ---------------------------

COVANCE INC.

By:   /s/ Charles C. Harwood, Jr.
      ---------------------------

Its:  Senior Vice President and Chief Financial Officer
      -------------------------------------------------

Date: October 28, 1999
      ---------------------------

The undersigned hereby agrees to be bound by the applicable provisions of
Sections 2(a), (c), (d) and 5 hereof.

BOEHRINGER INGELHEIM
PHARMACEUTICALS, INC.

By:   /s/ M. Haehl
      ---------------------------

Its:  Sr. VP Medical/DRA
      ---------------------------

Date: October 27, 1999
      ---------------------------

                                   Page 5 of 5

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