Document:

EXHIBIT 4.1
                                                                     -----------

                           VION PHARMACEUTICALS, INC.

                              AMENDED AND RESTATED
                             1993 STOCK OPTION PLAN

1.       Purpose.
         -------

         The purpose of this plan (the "Plan") is to secure for Vion
Pharmaceuticals, Inc. (the "Corporation") and its stockholders the benefits
arising from capital stock ownership by employees, officers and directors of,
and consultants or advisors to, the Corporation and its subsidiary corporations
who are expected to contribute to the Corporation's future growth and success.
Except where the context otherwise requires, the term "Corporation" shall
include all present and future subsidiaries of the Corporation as defined in
Sections 424(e) and 424(f) of the Internal Revenue Code of 1986, as amended or
replaced from time to time (the "Code"). Those provisions of the Plan which make
express reference to Section 422 shall apply only to Incentive Stock Options (as
that term is defined in the Plan).

2.       Type of Options and Administration.
         ----------------------------------

         (a) Types of Options. Options granted pursuant to the Plan shall be
authorized by action of the Board of Directors of the Corporation (or a
Committee designated by the Board of Directors) and may be either incentive
stock options ("Incentive Stock Options") meeting the requirements of Section
422 of the Code or non-statutory options which are not intended to meet the
requirements of Section 422 of the Code.

         (b) Administration. The Plan will be administered by the Board of
Directors of the Corporation, whose construction and interpretation of the terms
and provisions of the Plan shall be final and conclusive. The Board of Directors
may in its sole discretion grant options to purchase shares of the Corporation's
Common Stock, $.01 par value per share ("Common Stock") and issue shares upon
exercise of such options as provided in the Plan. The Board shall have
authority, subject to the express provisions of the Plan, to construe the
respective option agreements and the Plan, to prescribe, amend and rescind rules
and regulations relating to the Plan, to determine the terms and provisions of
the respective option agreements, which need not be identical, and to make all
other determinations in the judgment of the Board of Directors necessary or
desirable for the administration of the Plan. The Board of Directors may correct
any defect or supply any omission or reconcile any inconsistency in the Plan or
in any option agreement in the manner and to the extent it shall deem expedient
to carry the Plan into effect and it shall be the sole and final judge of such
expediency. No director or person acting pursuant to authority delegated by the
Board of Directors shall be liable for any action or determination under the
Plan made in good faith. The Board of Directors may, to the full extent
permitted by or consistent with applicable laws or regulations (including,
without limitation, applicable state law and Rule 16b-3 promulgated under the
Securities Exchange Act of 1934 (the "Exchange Act"), or any successor rule
("Rule 16b-3")), delegate any or all of its powers under the Plan to a committee
(the "Committee") appointed by the Board of Directors, and if the Committee is
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so appointed all references to the Board of Directors in the Plan shall mean and
relate to such Committee with respect to the powers so delegated.

         (c) Applicability of Rule 16b-3. Those provisions of the Plan which
make express reference to Rule 16b-3 shall apply to the Corporation only at such
time as the Corporation's Common Stock is registered under the Exchange Act,
subject to the last sentence of Section 3(b), and then only to such persons as
are required to file reports under Section 16(a) of the Exchange Act (a
"Reporting Person").

3.       Eligibility.
         -----------

         (a) General. Options may be granted to persons who are, at the time of
grant, employees, officers or directors of, or consultants or advisors to, the
Corporation; provided, that Incentive Stock Options may only be granted to
individuals who are employees of the Corporation (within the meaning of Section
3401(c) of the Code). A person who has been granted an option may, if he or she
is otherwise eligible, be granted additional options if the Board of Directors
shall so determine.

         (b) Grant of Options to Reporting Persons. From and after the
registration of the Common Stock of the Corporation under the Exchange Act, the
selection of a director or an officer who is a Reporting Person (as the terms
"director" and "officer" are defined for purposes of Rule 16b-3) as a recipient
of an option, the timing of the option grant, the exercise price of the option
and the number of shares subject to the option shall be determined either (i) by
the Board of Directors, of which all members shall be "disinterested persons"
(as hereinafter defined), or (ii) by a committee consisting of two or more
directors having full authority to act in the matter, each of whom shall be a
"disinterested person." For the purposes of the Plan, a director shall be deemed
to be a "disinterested person" only if such person qualifies as a "disinterested
person" within the meaning of Rule 16b-3, as such term is interpreted from time
to time. If at least two of the members of the Board of Directors do not qualify
as a "disinterested person" within the meaning of Rule 16b-3, as such term is
interpreted from time to time, then the granting of options to officers and
directors who are Reporting Persons under the Plan shall not be determined in
accordance with this Section 3(b) but shall be determined in accordance with the
other provisions of the Plan.

         (c) Directors' Options. Directors of the Company who are not employees
or beneficial owners of 5% or more of the outstanding Common Stock of the
Company ("Eligible Directors") and who are elected to the Board of Directors
subsequent to the date hereof will be granted an option ("Director Option") to
purchase 20,000 shares of Common Stock on the date that such person is first
elected or appointed a director (an "Initial Director Option"). Each Eligible
Director other than the Chairman of the Board will receive an automatic grant of
a Director Option to purchase 15,000 shares of Common Stock on the day
immediately following the date of each annual meeting of stockholders held
subsequent to December 31, 1998, as long as such director is a member of the

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<PAGE>

Board of Directors, and provided that such director did not receive an Initial
Director Option since the previous annual meeting of stockholders. The Chairman
of the Board, if an Eligible Director, will receive an automatic grant of a
Director Option to purchase 20,000 shares of Common Stock on the day immediately
following the date of each annual meeting of stockholders held subsequent to
December 31, 1998, as long as such director is a member of the Board of
Directors, and provided that such director did not receive an Initial Director
Option since the previous annual meeting of stockholders. The exercise price for
each share subject to a Director Option shall be equal to the fair market value
of the Common Stock on the date of grant. Director Options shall become
exercisable in four equal annual installments commencing one year from the date
the option is granted and will expire the earlier of 10 years after the date of
grant or 90 days after the termination of the director's service on the Board.
This Section 3(c) shall not be amended more than once every six months, other
than to comport with changes in the Internal Revenue Code, the Employee
Retirement Income Security Act, or the rules thereunder.

4.       Stock Subject to Plan.
         ---------------------

         The stock subject to options granted under the Plan shall be shares of
authorized but unissued or reacquired Common Stock. Subject to adjustment as
provided in Section 15 below, the maximum number of shares of Common Stock of
the Corporation which may be issued and sold under the Plan is 4,000,000 shares.
If an option granted under the Plan shall expire, terminate or is cancelled for
any reason without having been exercised in full, the unpurchased shares subject
to such option shall again be available for subsequent option grants under the
Plan.

5.       Forms of Option Agreements.
         --------------------------

         As a condition to the grant of an option under the Plan, each recipient
of an option shall execute an option agreement in such form not inconsistent
with the Plan as may be approved by the Board of Directors. Such option
agreements may differ among recipients.

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<PAGE>

6.       Purchase Price.
         --------------

         (a) General. The purchase price per share of stock deliverable upon the
exercise of an option shall be determined by the Board of Directors at the time
of grant of such option; provided, however, that in the case of an Incentive
Stock Option, the exercise price shall not be less than 100% of the Fair Market
Value (as hereinafter defined) of such stock, at the time of grant of such
option, or less than 110% of such Fair Market Value in the case of options
described in Section 11(b). "Fair Market Value" of a share of Common Stock of
the Corporation as of a specified date for the purposes of the Plan shall mean
the closing price of a share of the Common Stock on the principal securities
exchange on which such shares are traded on the day immediately preceding the
date as of which Fair Market Value is being determined, or on the next preceding
date on which such shares are traded if no shares were traded on such
immediately preceding day, or if the shares are not traded on a securities
exchange, Fair Market Value shall be deemed to be the average of the high bid
and low asked prices of the shares in the over-the-counter market on the day
immediately preceding the date as of which Fair Market Value is being determined
or on the next preceding date on which such high bid and low asked prices were
recorded. If the shares are not publicly traded, Fair Market Value of a share of
Common Stock (including in the case of any repurchase of shares, any
distributions with respect thereto which would be repurchased with the shares)
shall be determined in good faith by the Board of Directors. In no case shall
Fair Market Value be determined with regard to restrictions other than
restrictions which, by their terms, will never lapse.

         (b) Payment of Purchase Price. Options granted under the Plan may
provide for the payment of the exercise price by delivery of cash or a check to
the order of the Corporation in an amount equal to the exercise price of such
options, or, to the extent provided in the applicable option agreement, (i) by
delivery to the Corporation of shares of Common Stock of the Corporation having
a Fair Market Value on the date of exercise equal in amount to the exercise
price of the options being exercised, (ii) by any other means (including,
without limitation, by delivery of a promissory note of the optionee payable on
such terms as are specified by the Board of Directors) which the Board of
Directors determines are consistent with the purpose of the Plan and with
applicable laws and regulations (including, without limitation, the provisions
of Rule 16b-3 and Regulation T promulgated by the Federal Reserve Board) or
(iii) by any combination of such methods of payment.

7.       Option Period.
         -------------

         Subject to earlier termination as provided in the Plan, each option and
all rights thereunder shall expire on such date as determined by the Board of
Directors and set forth in the applicable option agreement, provided, that such
date shall not be later than (10) ten years after the date on which the option
is granted.

8.       Exercise of Options.
         -------------------

         Each option granted under the Plan shall be exercisable either in full
or in installments at such time or times and during such period as shall be set
forth in the option agreement evidencing such option, subject to the provisions
of the Plan. No option granted to a Reporting Person for purposes of the

                                      -4-
<PAGE>

Exchange Act, however, shall be exercisable during the first six months after
the date of grant. Subject to the requirements in the immediately preceding
sentence, if an option is not at the time of grant immediately exercisable, the
Board of Directors may (i) in the agreement evidencing such option, provide for
the acceleration of the exercise date or dates of the subject option upon the
occurrence of specified events, and/or (ii) at any time prior to the complete
termination of an option, accelerate the exercise date or dates of such option.
All options granted under the Plan will become exercisable in no fewer than four
equal annual installments commencing not earlier than the first anniversary of
the date of grant.

9.       Nontransferability of Options.
         -----------------------------

         No option granted under this Plan shall be assignable or otherwise
transferable by the optionee except by will or by the laws of descent and
distribution or pursuant to a qualified domestic relations order as defined in
the Code or Title I of the Employee Retirement Income Security Act, or the rules
thereunder. An option may be exercised during the lifetime of the optionee only
by the optionee. In the event an optionee dies during his employment by the
corporation or any of its subsidiaries, or during the three-month period
following the date of termination of such employment, his option shall
thereafter be exercisable, during the period specified to the full extent to
which such option was exercisable by the optionee at the time of his death
during the periods set forth in Section 10 or 11(d).

10.      Effect of Termination of Employment or Other Relationship.
         ---------------------------------------------------------

         Except as provided in Section 11(d) with respect to Incentive Stock
Options, and subject to the provisions of the Plan, an optionee may exercise an
option at any time within three (3) months following the termination of the
optionee's employment or other relationship with the Corporation or within one
(1) year if such termination was due to the death or disability of the optionee,
but, except in the case of the optionee's death, in no event later than the
expiration date of the Option. If the termination of the optionee's employment
is for cause or is otherwise attributable to a breach by the optionee of an
employment or confidentiality or non-disclosure agreement, the option shall
expire immediately upon such termination. The Board of Directors shall have the
power to determine what constitutes a termination for cause or a breach of an
employment or confidentiality or non-disclosure agreement, whether an optionee
has been terminated for cause or has breached such an agreement, and the date
upon which such termination for cause or breach occurs. Any such determinations
shall be final and conclusive and binding upon the optionee.

11.      Incentive Stock Options.
         -----------------------

         Options granted under the Plan which are intended to be Incentive Stock
Options shall be subject to the following additional terms and conditions:

         (a) Express Designation. All Incentive Stock Options granted under the
Plan shall, at the time of grant, be specifically designated as such in the
option agreement covering such Incentive Stock Options.

                                      -5-
<PAGE>

         (b) 10% Stockholder. If any employee to whom an Incentive Stock Option
is to be granted under the Plan is, at the time of the grant of such option, the
owner of stock possessing more than 10% of the total combined voting power of
all classes of stock of the Corporation (after taking into account the
attribution of stock ownership rules of Section 424(d) of the Code), then the
following special provisions shall be applicable to the Incentive Stock Option
granted to such individual:

                  (i) The purchase price per share of the Common Stock subject
         to such Incentive Stock Option shall not be less than 110% of the Fair
         Market Value of one share of Common Stock at the time of grant; and

                 (ii) the option exercise period shall not exceed five years
         from the date of grant.

         (c) Dollar Limitation. For so long as the Code shall so provide,
options granted to any employee under the Plan (and any other incentive stock
option plans of the Corporation) which are intended to constitute Incentive
Stock Options shall not constitute Incentive Stock Options to the extent that
such options, in the aggregate, become exercisable for the first time in any one
calendar year for shares of Common Stock with an aggregate Fair Market Value, as
of the respective date or dates of grant, of more than $100,000.

         (d) Termination of Employment, Death or Disability. No Incentive Stock
Option may be exercised unless, at the time of such exercise, the optionee is,
and has been continuously since the date of grant of his or her option, employed
by the Corporation, except that:

                  (i) an Incentive Stock Option may be exercised within the
         period of three months after the date the optionee ceases to be an
         employee of the Corporation (or within such lesser period as may be
         specified in the applicable option agreement), provided, that the
         agreement with respect to such option may designate a longer exercise
         period and that the exercise after such three-month period shall be
         treated as the exercise of a non-statutory option under the Plan;

                  (ii) if the optionee dies while in the employ of the
         Corporation, or within three months after the optionee ceases to be
         such an employee, the Incentive Stock Option may be exercised by the
         person to whom it is transferred by will or the laws of descent and
         distribution within the period of one year after the date of death (or
         within such lesser period as may be specified in the applicable option
         agreement); and

                  (iii) if the optionee becomes disabled (within the meaning of
         Section 22(e)(3) of the Code or any successor provisions thereto) while
         in the employ of the Corporation, the Incentive Stock Option may be
         exercised within the period of one year after the date the optionee
         ceases to be such an employee because of such disability (or within
         such lesser period as may be specified in the applicable option
         agreement).

                                      -6-
<PAGE>

For all purposes of the Plan and any option granted hereunder, "employment"
shall be defined in accordance with the provisions of Section 1.421-7(h) of the
Incoming Tax Regulations (or any successor regulations). Notwithstanding the
foregoing provisions to Incentive Stock Option may be exercised after its
expiration date.

12.      Additional Provisions.
         ---------------------

         (a) Additional Option Provisions. The Board of Directors may, in its
sole discretion, include additional provisions in option agreements covering
options granted under the Plan, including without limitation restrictions on
transfer, repurchase rights, rights of first refusal, commitments to pay cash
bonuses, to make, arrange for or guaranty loans or to transfer other property to
optionees upon exercise of options, or such other provisions as shall be
determined by the Board of Directors; provided, that such additional provisions
shall not be inconsistent with any other term or condition of the Plan and such
additional provisions shall not cause any Incentive Stock Option granted under
the Plan to fail to qualify as an Incentive Stock Option within the meaning of
Section 422 of the Code.

         (b) Acceleration, Extension, Etc. The Board of Directors may, in its
sole discretion, (i) accelerate the date or dates on which all or any particular
option or options granted under the Plan may be exercised or (ii) extend the
dates during which all, or any particular, option or options granted under the
Plan may be permitted if it would cause the Plan to fail to comply with Section
422 of the Code or with Rule 16b-3 (if applicable).

13.      General Restrictions.
         --------------------

         (a) Investment Representations. The Corporation may require any person
to whom an option is granted, as a condition of exercising such option, to give
written assurances in substance and form satisfactory to the Corporation to the
effect that such person is acquiring the Common Stock subject to the option for
his or her own account for investment and not with any present intention of
selling or otherwise distributing the same, and to such other effects as the
Corporation deems necessary or appropriate in order to comply with federal and
applicable state securities laws, or with covenants or representations made by
the Corporation in connection with any public offering of its Common Stock.

         (b) Compliance with Securities Law. Each option shall be subject to the
requirement that if, at any time, counsel to the Corporation shall determine
that the listing, registration or qualification of the shares subject to such
option upon any securities exchange or under any state or federal law, or the
consent or approval of any governmental or regulatory body, or that the
disclosure of non-public information or the satisfaction of any other condition
is necessary as a condition of, or in connection with the issuance or purchase
of shares thereunder, such option may not be exercised, in whole or in part,
unless such listing, registration, qualification, consent or approval, or
satisfaction of such condition shall have been effected or obtained on
conditions acceptable to the Board of Directors. Nothing herein shall be deemed
to require the Corporation to apply for or to obtain such listing, registration
or qualification, or to satisfy such condition.

                                      -7-
<PAGE>

14.      Rights as a Stockholder.
         -----------------------

         The holder of an option shall have no rights as a stockholder with
respect to any shares covered by the option (including, without limitation, any
rights to receive dividends or non-cash distributions with respect to such
shares) until the date of issue of a stock certificate to him or her for such
shares. No adjustment shall be made for dividends or other rights for which the
record date is prior to the date such stock certificate is issued.

15.      Adjustment Provisions for Recapitalization, Reorganizations and Related
         -----------------------------------------------------------------------
         Transactions.
         ------------

         (a) Recapitalization and Related Transactions. If, through or as a
result of any recapitalization, reclassification, stock dividend, stock split,
reverse stock split or other similar transaction, (i) the outstanding shares of
Common Stock are increased, decreased or exchanged for a different number or
kind of shares or other securities of the Corporation, or (ii) additional shares
or new or different shares or other non-cash assets are distributed with respect
to such shares of Common Stock or other securities, an appropriate and
proportionate adjustment shall be made in (x) the maximum number and kind of
shares reserved for issuance under the Plan, (y) the number and kind of shares
or other securities subject to any then outstanding options under the Plan, and
(z) the price for each share subject to any then outstanding options under the
Plan, without changing the aggregate purchase price as to which such options
remain exercisable. Notwithstanding the foregoing, no adjustment shall be made
pursuant to this Section 15 if such adjustment (i) would cause the Plan to fail
to comply with Section 422 of the Code or with Rule 16b-3 or (ii) would be
considered as the adoption of a new plan requiring stockholder approval.

         (b) Reorganization, Merger and Related Transactions. If the Corporation
shall be the surviving corporation in any reorganization, merger or
consolidation of the Corporation with one or more other corporations, any then
outstanding option granted pursuant to the Plan shall pertain to and apply to
the securities to which a holder of the number of shares of Common Stock subject
to such options would have been entitled immediately following such
reorganization, merger, or consolidation, with a corresponding proportionate
adjustment of the purchase price as to which such options may be exercised so
that the aggregate purchase price as to which such options may be exercised
shall be the same as the aggregate purchase price as to which such options may
be exercised for the shares remaining subject to the options immediately prior
to such reorganization, merger, or consolidation.

         (c) Board Authority to Make Adjustments. Any adjustments made under
this Section 15 will be made by the Board of Directors, whose determination as
to what adjustments, if any, will be made and the extent thereof will be final,
binding and conclusive. No fractional shares will be issued under the Plan on
account of any such adjustments.

16.      Merger, Consolidation, Asset Sale, Liquidation, Etc.
         ---------------------------------------------------

                  (a) General. In the event of a consolidation or merger in
which the Corporation is not the surviving corporation, or sale of all or
substantially all of the assets of the Corporation in which outstanding shares
of Common Stock are exchanged for securities, cash or other property of any
other corporation or business entity or in the event of a liquidation of the

                                      -8-
<PAGE>

Corporation (collectively, a "Corporate Transaction"), the Board of Directors of
the Corporation, or the board of directors of any corporation assuming the
obligations of the Corporation, may, in its discretion, take any one or more of
the following actions, as to outstanding options: (i) provide that such options
shall be assumed, or equivalent options shall be substituted, by the acquiring
or succeeding corporation (or an affiliate thereof), provided that any such
options substituted for Incentive Stock Options shall meet the requirements of
Section 424(a) of the Code, (ii) upon written notice to the optionees, provide
that all unexercised options will terminate immediately prior to the
consummation of such transaction unless exercised by the optionee within a
specified period following the date of such notice, (iii) in the event of a
Corporate Transaction under the terms of which holders of the Common Stock of
the Corporation will receive upon consummation thereof a cash payment for each
share surrendered in the Corporate Transaction (the "Transaction Price"), make
or provide for a cash payment to the optionees equal to the difference between
(A) the Transaction Price times the number of shares of Common Stock subject to
such outstanding options (to the extent then exercisable at prices not in excess
of the Transaction Price) and (B) the aggregate exercise price of all such
outstanding options in exchange for the termination of such options, and (iv)
provide that all or any outstanding options shall become exercisable in full
immediately prior to such event.

         (b) Substitute Options. The Corporation may grant options under the
Plan in substitution for options held by employees of another corporation who
become employees of the Corporation, or a subsidiary of the Corporation, as the
result of a merger or consolidation of the employing corporation with the
Corporation or a subsidiary of the Corporation, or as a result of the
acquisition by the Corporation, or one of its subsidiaries, of property or stock
of the employing corporation. The Corporation may direct that substitute options
be granted on such terms and conditions as the Board of Directors considers
appropriate in the circumstances.

17.      No Special Employment Rights.
         ----------------------------

         Nothing contained in the Plan or in any option shall confer upon any
optionee any right with respect to the continuation of his or her employment by
the Corporation or interfere in any way with the right of the Corporation at any
time to terminate such employment or to increase or decrease the compensation of
the optionee.

18.      Other Employee Benefits.
         -----------------------

         Except as to plans which by their terms include such amounts as
compensation, the amount of any compensation deemed to be received by an
employee as a result of the exercise of an option or the sale of shares received
upon such exercise will not constitute compensation with respect to which any
other employee benefits of such employee are determined, including, without
limitation, benefits under any bonus, pension, profit-sharing, life insurance or
salary continuation plan, except as otherwise specifically determined by the
Board of Directors.

                                      -9-
<PAGE>

19.      Amendment of the Plan.
         ---------------------

         (a) The Board of Directors may at any time, and from time to time,
modify or amend the Plan in any respect, except that if at any time the approval
of the stockholders of the Corporation is required under Section 422 of the Code
or any successor provision with respect to Incentive Stock Options, or under
Rule 16b-3, the Board of Directors may not effect such modification or amendment
without such approval.

         (b) The termination or any modification or amendment of the Plan shall
not, without the consent of an optionee, affect his or her rights under an
option previously granted to him or her. With the consent of the optionee
affected, the Board of Directors may amend outstanding option agreements in a
manner not inconsistent with the Plan. The Board of Directors shall have the
right to amend or modify (i) the terms and provisions of the Plan and of any
outstanding Incentive Stock Options granted under the Plan to the extent
necessary to qualify any or all such options for such favorable federal income
tax treatment (including deferral of taxation upon exercise) as may be afforded
incentive stock options under Section 422 of the Code and (ii) the terms and
provisions of the Plan and of any outstanding option to the extent necessary to
ensure the qualification of the Plan under Rule 16b-3.

20.      Withholding.
         -----------

         (a) The Corporation shall have the right to deduct from payments of any
kind otherwise due to the optionee any federal, state or local taxes of any kind
required by law to be withheld with respect to any shares issued upon exercise
of options under the Plan. Subject to the prior approval of the Corporation,
which may be withheld by the Corporation in its sole discretion, the optionee
may elect to satisfy such obligations, in whole or in part, (i) by causing the
Corporation to withhold shares of Common Stock otherwise issuable pursuant to
the exercise of an option or (ii) by delivering to the Corporation shares of
Common Stock already owned by the optionee. The shares so delivered or withheld
shall have a Fair Market Value equal to such withholding obligation as of the
date that the amount of tax to be withheld is to be determined. An optionee who
has made an election pursuant to this Section 20(a) may only satisfy his or her
withholding obligation with shares of Common Stock which are not subject to any
repurchase, forfeiture, unfulfilled vesting or other similar requirements.

         (b) The acceptance of shares of Common Stock upon exercise of an
Incentive Stock Option shall constitute an agreement by the optionee (i) to
notify the Corporation if any or all of such shares are disposed of by the
optionee within two years from the date the option was granted or within one
year from the date the shares were transferred to the optionee pursuant to the
exercise of the option, and (ii) if required by law, to remit to the
Corporation, at the time of and in the case of any such disposition, an amount
sufficient to satisfy the Corporation's federal, state and local withholding tax
obligations with respect to such disposition, whether or not, as to both (i) and
(ii), the optionee is in the employ of the Corporation at the time of such
disposition.

         (c) Notwithstanding the foregoing, in the case of a Reporting Person
whose options have been granted in accordance with the provisions of Section
3(b) herein, no election to use shares for the payment of withholding taxes
shall be effective unless made in compliance with any applicable requirements of
Rule 16b-3.

                                      -10-
<PAGE>

21.      Cancellation and New Grant of Options, Etc.
         -------------------------------------------

         The Board of Directors shall have the authority to effect, at any time
and from time to time, with the consent of the affected optionees, (i) the
cancellation of any or all outstanding options under the Plan and the grant in
substitution therefor of new options under the Plan covering the same or
different numbers of shares of Common Stock and having an option exercise price
per share which may be lower or higher than the exercise price per share of the
cancelled options or (ii) the amendment of the terms of any and all outstanding
options under the Plan to provide an option exercise price per share which is
higher or lower than the then current exercise price per share of such
outstanding options.

22.      Effective Date and Duration of the Plan.
         ---------------------------------------

         (a) Effective Date. The Plan shall become effective when adopted by the
Board of Directors, but no Incentive Stock Option granted under the Plan shall
become exercisable unless and until the Plan shall have been approved by the
Corporation's stockholders. If such stockholder approval is not obtained within
twelve (12) months after the date of the Board's adoption of the Plan, no
options previously granted under the Plan shall be deemed to be Incentive Stock
Options and no Incentive Stock Options shall be granted thereafter. Amendments
to the Plan not requiring stockholder approval shall become effective when
adopted by the Board of Directors; amendments requiring stockholder approval (as
provided in Section 19) shall become effective when adopted by the Board of
Directors, but no Incentive Stock Option granted after the date of such
amendment shall become exercisable (to the extent that such amendment to the
Plan was required to enable the Corporation to grant such Incentive Stock Option
to a particular optionee) unless and until such amendment shall have been
approved by the Corporation's stockholders. If such stockholder approval is not
obtained within twelve (12) months of the Board's adoption of such amendment,
any Incentive Stock Options granted on or after the date of such amendment shall
terminate to the extent that such amendment to the Plan was required to enable
the Corporation to grant such option to a particular optionee. Subject to this
limitation, options may be granted under the Plan at any time after the
effective date and before the date fixed for termination of the Plan.

         (b) Termination. Unless sooner terminated in accordance with Section
16, the Plan shall terminate upon the earlier of (i) the close of business on
the day next preceding the tenth anniversary of the date of is adoption by the
Board of Directors, or (ii) the date on which all shares available for issuance
under the Plan shall have been issued pursuant to the exercise or cancellation
of options granted under the Plan. If the date of termination is determined
under (i) above, then options outstanding on such date shall continue to have
force and effect in accordance with the provisions of the instruments evidencing
such options.

23.      Provision for Foreign Participants.
         ----------------------------------

         The Board of Directors may, without amending the Plan, modify awards or
options granted to participants who are foreign nationals or employed outside
the United States to recognize differences in laws, rules, regulations or
customs of such foreign jurisdictions with respect to tax, securities, currency,
employee benefit or other matters.

                                      -11-
<PAGE>

24.      Governing Law.
         -------------

         The provisions of this Plan shall be governed and construed in
accordance with the laws of the State of New York without regard to the
principles of conflicts of laws.

                                    Originally Adopted by the Board of Directors
                                    on April 15, 1993

                                      -12-EXHIBIT 4.2
                                                                     -----------

                           VION PHARMACEUTICALS, INC.

                             STOCK OPTION AGREEMENT

                  THIS AGREEMENT, made as of the ___ day of ____, 2000 by and
between VION PHARMACEUTICALS, INC., a Delaware corporation (the "Company"), and,
______________________________ , (the "Holder"):

                  The Board of Directors (the "Board") has determined that it
would be to the advantage and interest of the Company to grant the option
provided for herein to the Holder for services rendered for the benefit of the
Company.

                  NOW, THEREFORE, the Company, with the approval of the Board,
hereby grants to the Holder, as of the date hereof, pursuant to the terms of the
Company's Amended and Restated 1993 Stock Option Plan (the terms of which are
incorporated by reference herein), an incentive stock option to purchase all or
any part of __________ shares of Common Stock of the Company, par value $.01 per
share, at a price per share of $ _____ (the "Option"), and upon the following
terms and conditions:

                  1. (a) The Option shall expire on the tenth anniversary of the
date hereof, unless sooner terminated as provided herein (the "Expiration
Date").

                     (b) Commencing ________________ , the Holder may exercise
25% of the Option, and an additional 25% of the Option may be exercised on a
cumulative basis commencing at the end of each 12 month period thereafter, such
that 100% of the Option may be exercised on ___________ ; provided, that the
Option may be exercised in full upon a "Change in Control" (as described below).
A "Change in Control" of the Company shall be deemed to have occurred if

         (i) any "person" (as such term is defined in Section 3(a)(9) of the
         Securities Exchange Act of 1934, as amended (the "Exchange Act") and as
         modified and used in Sections 13(d) and 14(d) of the Exchange Act)
         other than (A) the Company or any of its subsidiaries, (B) any trustee
         or other fiduciary holding securities under an employee benefit plan of
         the Company or any of its subsidiaries, (C) an underwriter temporarily
         holding securities pursuant to an offering of such securities, or (D)
         any corporation, owned, directly or indirectly, by the stockholders of
         the Company in substantially the same proportions as their ownership of
         stock of the Company (a "Person"), is or becomes the "beneficial owner"
         (as defined in Rule 13d-3 under the Exchange Act), directly or
         indirectly, of securities of the Company representing 40% or more of
         the combined voting power of the Company's then outstanding securities;
<PAGE>

         (ii) during any period of two consecutive years (not including any
         period prior to the execution of this Agreement), individuals who at
         the beginning of such period constitute the Board of Directors of the
         Company, and any new director (other than a director designated by a
         person who has entered into an agreement with the Company to effect a
         transaction described in clause (i), (iii) or (iv) of this Section)
         whose election by the Board of Directors of the Company or nomination
         for election by the Company's stockholders was approved by a vote of at
         least two-thirds (2/3) of the directors then still in office who either
         were directors at the beginning of the period or whose election or
         nomination for election was previously approved, cease for any reason
         to constitute at least a majority of the Company's Board of Directors;

         (iii) the stockholders of the Company approve a merger or consolidation
         of the Company with any other corporation, other than (A) a merger or
         consolidation that would result in the voting securities of the Company
         outstanding immediately prior thereto continuing to represent (either
         by remaining outstanding or by being converted into voting securities
         of the surviving entity), in combination with the ownership of any
         trustee or other fiduciary holding securities under an employee benefit
         plan of the Company, at least 60% of the combined voting power of the
         voting securities of the Company or such surviving entity outstanding
         immediately after such merger or consolidation, or (B) merger or
         consolidation effected to implement a recapitalization of the Company
         (or similar transaction) in which no Person acquires more than 50% of
         the combined voting power of the Company's then outstanding securities;
         or

         (iv) the stockholders of the Company approve a plan of complete
         liquidation of the Company or an agreement for the sale or disposition
         of the Company or all or substantially all of the Company's assets.

         2. (a) The Holder may exercise the Option with respect to all or any
part of the shares then purchasable hereunder by giving the Company written
notice of such exercise in the form annexed, as provided in paragraph 8 hereof.
Such notice shall specify the number of shares as to which the Option is being
exercised and shall be accompanied by payment in full in cash of an amount equal
to the exercise price of such shares multiplied by the number of shares as to
which the Option is being exercised; provided that, if permitted by the Board,
the purchase price may be paid, in whole or in part, by surrender or delivery to
the Company of Common Stock of the Company having a fair market value on the
date of the exercise equal to the portion of the purchase price being so paid.
In such event, fair market value shall be determined as follows. If, at the time
an Option is granted, the Common Stock is publicly traded, such fair market
value shall be the closing price (or the mean of the latest bid and asked
prices) of a share of Common Stock on such date as reported in The Wall Street
Journal (or a publication or reporting service deemed equivalent to The Wall
Street Journal for such purpose by the Board). If the Board shall determine such
stock price quotation is not representative of fair market value by reason of
the lack of a significant number of recent transactions or otherwise, the Board
may determine fair market value in such a manner as it shall deem appropriate
under the circumstances. If, at the time an Option is exercised, the Common
Stock is not publicly traded, the Board shall make a good faith attempt to
determine such fair market value.

                                                                               2
<PAGE>

                  (b) Prior to, or concurrently with, delivery by the Company to
the Holder of a certificate(s) representing such shares, the Holder shall, upon
notification of the amount due, pay promptly any amount necessary to satisfy
applicable federal, state or local withholding tax requirements. In the event
such amount is not paid promptly, the Company shall have the right to apply from
the purchase price paid (including payment in Common Stock) any taxes required
by law to be withheld by the Company with respect to such payment and the number
of shares to be issued by the Company will be reduced accordingly. Furthermore,
if permitted by the Board, the Company may, at the Holder's request, undertake
to pay any taxes required to be paid by the Holder as a consequence of the
exercise of the Option (and as to which the Company does not have a withholding
obligation), provided the Holder surrenders or delivers to the Company Common
Stock having a fair market value (determined in accordance with paragraph 2(a)
above) on the date of the exercise of the Option equal to the amount of the
taxes payable by the Holder.

         3. In the event of a change in the outstanding Common Stock of the
Company by reason of a stock dividend, split-up, reverse split,
recapitalization, merger, consolidation, combination or exchange of shares,
spin-off, reorganization, liquidation or the like, then the aggregate number of
shares and price per share subject to the Option shall be appropriately adjusted
by the Board, whose determination shall be conclusive.

         4. The Option shall not be transferable other than by will or by the
laws of descent and distribution. Any attempt by the Holder to transfer, assign,
pledge, hypothecate or otherwise dispose of this Option or of any right
hereunder, or in the event of the levy or any attachment, execution or similar
process upon the rights or interest hereby conferred, the Company may terminate
this option by notice to the Holder and it shall thereupon become null and void.

         5. In the event the Holder shall become permanent and totally disabled
within the meaning of Section 22 (e) (3) of the Internal Revenue Code of 1986,
as amended, and not be able to exercise the Option, or if the Holder shall die,
then the Option may be exercised as set forth herein by the person or persons to
whom the Holder's rights under the Option pass by will or applicable law, or if
no such person has such right, by his personal representatives, at any time
prior to the Expiration Date.

         6. Neither the Holder nor, in the event of his death or disability, any
person entitled to exercise his rights hereunder, shall have any of the rights
of a stockholder with respect to the shares subject to the Option until share
certificates have been issued and registered in the name of the Holder, his
personal representative(s) or his estate, as the case maybe.

         7. The Holder hereby represents and warrants to the Company that he
understands that:

                  (a) the Option has not been registered under the Securities
Act of 1993 (the "Securities Act") or any state securities laws ("State Laws");

                  (b) the Option may not be exercised unless the shares of
Common Stock to be issued upon such exercise have been registered under the
Securities Act and State Laws or counsel to the Company is satisfied that an
exemption from registration is available (which may be conditioned upon the

                                                                               3
<PAGE>

Company receiving certain information from and agreements of the Holder and the
Holder satisfying certain suitability standards or other requirements imposed by
law);

                  (c) the Option and any Common Stock purchased upon exercise of
the Option cannot be sold or otherwise disposed of unless they are subsequently
registered under the Securities Act and applicable State Laws or counsel to the
Company is satisfied that an exemption from registration is available; and

                  (d) neither the Holder nor any person entitled to exercise his
rights will have any right to require that the Option or such Common Stock be
registered under the Securities Act or State Laws.

         8. Any notice to the Company provided for in this Agreement shall be
addressed to the Company in care of its Treasurer, Thomas E. Klein, c/o Vion
Pharmaceuticals, Inc., 4 Science Park, New Haven, Connecticut 06511, and any
notice to the Holder shall be addressed to him at his address now on file with
the Company, or to such other address as either may last have designated to the
other by notice as provided herein. Notice may be given by hand delivery
(including federal express or an equivalent overnight delivery service), by
facsimile transmission, with receipt confirmed, or by registered or certified
mail. Any notice given by hand or facsimile shall be deemed to be given on the
date of delivery or transmission, and any notice mailed by registered or
certified mail shall be deemed to be given on the third business day after
mailing.

         9. In the event that any question or controversy shall arise with
respect to the nature, scope or extent of any one or more rights conferred by
this Option, the determination by the Board (as constituted at the time of such
determination) of the rights of the Holder shall be conclusive, final and
binding upon the Holder and upon any other person who shall assert any right
pursuant to this Stock Option Agreement.

                                              VION PHARMACEUTICALS, INC.

                                              By:  _____________________________
                                                       Name:
                                                       Title:

ACCEPTED AND AGREED:

------------------------

                                                                               4

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