<PAGE>

                                                                     Exhibit 4.1

                                ACETO CORPORATION
                             2002 STOCK OPTION PLAN
SECTION 1. PURPOSE.

         Aceto Corporation ("Aceto" or the "Company") hereby establishes the
Aceto Corporation 2002 Stock Option Plan. The purposes of the Aceto Corporation
2002 Stock Option Plan (the "Plan"), are to attract, retain and motivate
Eligible Participants, as defined below, to compensate them for their
contributions to the Company's growth and profit and to encourage them to own
the Company's common stock, thereby promoting the interests of the Company and
its stockholders.

SECTION 2. DEFINITIONS.

         As used in the Plan, the following terms shall have the meanings set
forth below:

         "Affiliate" shall mean (i) any entity that, directly or indirectly, is
controlled by the Company; (ii) a subsidiary of the Company; and (iii) any
entity in which the Company has a significant equity or business interest, in
each case as determined by the Board.

         "Award" shall mean any Option, Restricted Stock Award, or other
stock-based Award.

         "Award Agreement" shall mean any written instrument or document
evidencing any Award, which may, but need not be, executed by an Eligible
Participant.

         "Board" shall mean the Board of Directors of the Company.

         "Change in Control" shall be deemed to have occurred if: (i) any
"person" as such term is used in Sections 13(d) and 14(d) of the Exchange Act
(other than the Company, any trustee or other fiduciary holding securities under
any employee benefit plan of the Company,) 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 20% or more of the voting power of the
Company's then outstanding securities; (ii) during any period of two consecutive
years, individuals who at the beginning of such period constitute the Board of
Directors, 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 paragraph) whose election by the
Board of Directors or nomination for election by the Company's stockholders was
approved by a vote of at least two-thirds of the directors then still in office
who either were directors at the beginning of the two year period or whose
election or nomination for election was previously so approved, cease for any
reason to constitute at least a majority of the Board of Directors; (iii) the
stockholders of the Company approve a merger or consolidation of the Company
with any other corporation, other than 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) more than 50% of the
combined voting power of the voting securities of the Company or such surviving
entity outstanding immediately after such merger or consolidation; provided,
however, that a merger or consolidation effected to implement a recapitalization
of the Company (or similar transaction) in which no person acquires more than
20% of the combined voting power of the Company's then outstanding securities
shall not constitute a change in Control of the Company; or (iv) the
stockholders of the Company approve a plan of complete liquidation of the
Company or an agreement for the sale or disposition by the Company of all or
substantially all of the Company's assets. If any of the events enumerated in
clauses (i) through (iv) occur the Board shall determine the effective date of
the Change in Control resulting therefrom, for purposes of the Plan.

         "Code" shall mean the Internal Revenue Code of 1986, as amended from
time to time, and the rules and regulations promulgated thereunder.

<PAGE>

         "Committee" shall mean a committee of the Board designated by the Board
to make recommendations to the Board with regard to Awards. Until otherwise
determined by the Board, the Executive Committee of the Board (which serves as
the Executive Compensation Committee) shall be the Committee under the Plan.

         "Common Stock" shall mean shares of the Company's common stock, $.01
par value.

         "Eligible Participant" shall mean an employee of the Company or any
Affiliate. Such term shall also mean any non-employee director, adviser,
consultant or independent contractor to the Company or any Affiliate, and any
reference to employment or termination of employment under the Plan shall be
deemed to apply to such director, adviser, consultant or independent contractor,
for the purpose of the Plan only, as if the services of such person constitute
employment services.

         "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended.

         "Executive Officer" shall mean, at any time, an individual who is an
executive officer of the Company within the meaning of Exchange Act Rule 3b-7
promulgated and interpreted by the SEC under the Exchange Act, or any successor
rule or regulation thereto as in effect from time to time, or who is an officer
of the Company within the meaning of Exchange Act Rule 16a-1(f) as promulgated
and interpreted by the SEC under the Exchange Act, or any successor rule or
regulation thereto as in effect from time to time.

         "Fair Market Value" of a share of the Company's Common Stock for any
purpose on a particular date shall be the last reported sale price per share of
Common Stock on the principal stock exchange on which the Common Stock is
traded, or if such exchange was closed on such day, or if it was open but no
such sale took place on such day, then on the preceding day that the Common
Stock was traded on such exchange.

         "Incentive Stock Option" shall mean an Option which meets the
requirements of Section 422 of the Code.

         "Non-Qualified Stock Option" shall mean an Option which does not meet
the requirements of Section 422 of the Code.

         "Option" shall mean an Incentive Stock Option or Non-Qualified Stock
Option.

         "Participant" shall mean any Eligible Participant selected by the Board
to receive an Award under the Plan.

         "Person" shall mean any individual, corporation, partnership,
association, joint-stock company, trust, unincorporated organization, government
or political subdivision thereof or other entity.

         "QDRO" shall mean a domestic relations order meeting such requirements
as the Committee shall determine, in its sole discretion.

"Restricted Stock" shall mean any Share granted under Section 7 of the Plan.

         "SEC" shall mean the Securities and Exchange Commission or any
successor thereto and shall include the staff thereof.

         "Shares" shall mean shares of the Common Stock, $ .01 par value, of the
Company.

SECTION 3. ADMINISTRATION.

         (a) AUTHORITY OF COMMITTEE. The Committee shall, subject to the terms
of the Plan and applicable law, make recommendations to the Board with regard to
(i) designation of Participants; (ii) the type or types of Awards to be granted
to an Eligible Participant; (iii) the number of Shares to be covered by Awards;
(iv) terms and conditions of Awards; and (v) unless otherwise expressly provided
in the Plan, designations, determination, interpretations, and suggested
decisions with respect to the Plan or any Award.

<PAGE>

         (b) AUTHORITY OF BOARD. All Awards under the Plan shall be made by the
Board, which shall have full authority to accept, reject or modify any
recommendations of the Committee. All designations, determinations,
interpretations, and other decisions under or with respect to the Plan or any
Award shall be within the sole discretion of the Board, may be made at any time
and shall be final, conclusive, and binding upon all Persons, including the
Company, any Affiliate, any Participant, any holder or beneficiary of any Award,
and any stockholder.

SECTION 4. SHARES AVAILABLE FOR AWARDS.

         (a) SHARES AVAILABLE. Subject to adjustment as provided in Section
4(b), the number of Shares with respect to which Awards may be granted under the
Plan shall be five hundred thousand (500,000). If, after the effective date of
the Plan, any Shares covered by an Award granted under the Plan are forfeited,
or if such an Award terminates or is canceled without the delivery of shares,
then the Shares covered by such Award, or the number of Shares otherwise counted
against the aggregate number of Shares with respect to which Awards may be
granted, to the extent of any such forfeiture, termination or cancellation,
shall again become Shares with respect to which Awards may be granted. In the
event that any Option or other Award granted hereunder is exercised through the
delivery of Shares or in the event that withholding tax liabilities arising from
such Award are satisfied by the withholding of Shares by the Company, the number
of Shares available for Awards under the Plan shall be increased by the number
of Shares so surrendered or withheld.

         (b) ADJUSTMENTS. In the event that any dividend (other than regular
dividends) or other distribution (whether in the form of cash, Shares, other
securities, or other property), recapitalization, stock split, reverse stock
split, reorganization, merger, consolidation, split-up, spin-off, combination,
repurchase, or exchange of Shares, or other similar corporate transaction or
event affects the Shares such that an adjustment is appropriate in order to
prevent dilution or enlargement of the benefits or potential benefits intended
to be made available under the Plan, then adjustment shall be made, in such
manner as shall be equitable, of (i) the number of Shares with respect to which
Awards may be granted, (ii) the number of Shares subject to outstanding Awards,
and (iii) the grant or exercise price with respect to any Award, provided, that
with respect to any Award no such adjustment shall be made to the extent that
such adjustment would be inconsistent with the Plan's meeting the requirements
of Section 162(m) of the Code, as from time to time amended.

         (c) Sources of Shares Deliverable under Awards. Any Shares delivered
pursuant to an Award may consist, in whole or in part, of authorized and
unissued Shares or of treasury Shares.

SECTION 5. ELIGIBILITY.

         Any employee (including an officer, Executive Officer or director) of
the Company or any Affiliate, including any non-employee director, advisor,
consultant or independent contractor to the Company or any Affiliate, shall be
an Eligible Participant. To the extent the Board deems it necessary, appropriate
or desirable to comply with foreign law or practice and to further the purpose
of this Plan, the Board may, without amending this Plan, (i) establish rules
applicable to Awards granted to Participants who are foreign nationals, are
employed outside the United States, or both, including rules that differ from
those set forth in this Plan, and (ii) grant Awards to such Participants in
accordance with those rules.

SECTION 6. STOCK OPTIONS - TERMS AND CONDITIONS.

         All Options granted under the Plan shall be either Incentive Stock
Options or Non-Qualified Stock Options and shall be evidenced by Award
Agreements which shall be subject to applicable provisions of the Plan and such
other provisions as they may contain including:

         (a) PRICE. The exercise price per Share shall not be less than 100% of
the Fair Market Value of a Share on the date of Award.

<PAGE>

         (b) PERIOD. The Board, upon recommendation of the Committee may
establish the term of any Option award under the Plan, provided, however, that
an Option shall expire no later than 10 years from the date of Award, and may
not be exercisable less than six months from the date it is granted.

         (c) TIME OF EXERCISE. The Board, upon recommendation of the Committee,
may grant Options to Participants with vesting schedules based on the Company's
publicly traded share price exceeding predetermined levels for designated
periods of time, and/or the passage of time, such that the Option becomes fully
exercisable in a series of installments. The Board, upon recommendation of the
Committee, may also establish other conditions of exercise and may accelerate
the exercisability of any Option granted to a Participant under the Plan.

         (d) PAYMENT. No Shares shall be delivered pursuant to any exercise of
an Option until payment in full of the option price in cash, or its equivalent,
or by exchanging Shares owned by the optionee (which are not the subject of any
pledge or other security interest), or by a combination of the foregoing,
provided that the combined value of all cash and cash equivalents and the Fair
Market Value of any such Shares so tendered to the Company as of the date of
such tender is at least equal to such option price.

         (e) EXERCISE. An Option, or portion thereof, shall be exercised by
delivery of a written notice of exercise to the Company. A Participant shall not
have any of the rights or privileges of the holder of Common Stock until such
time as Shares of Common Stock are issued or transferred to the Participant.

         (f) RESTRICTIONS ON INCENTIVE STOCK OPTIONS. The aggregate Fair Market
Value (determined as of the Grant Date) of shares of Common Stock with respect
to which all Incentive Stock Options first become exercisable by any grantee in
any calendar year under this or another plan of the Company and its Affiliates
may not exceed $100,000 or such other amount as may be permitted from time to
time under Section 422 of the Code. To the extent that such aggregate Fair
Market Value shall exceed $100,000, or other applicable amount, such Options
(taking Options into account in the order in which they were granted) shall be
treated as Non-Qualified Stock Options. In such case, the corporation may
designate the shares of Common Stock that are to be treated as stock acquired
pursuant to the exercise of any Incentive Stock Option by issuing a separate
certificate for such shares and identifying the certificate as Incentive Stock
Option shares in the stock transfer records of the Company.

         The exercise price of any Incentive Stock Option granted to a grantee
who owns (within the meaning of Section 422(b)(6) of the Code, after the
application of the attribution rules in Section 424(d) of the Code) more than
10% of the total combined voting power of all classes of shares of the
Corporation or its Parent or Subsidiary corporations (within the meaning of
Sections 422 and 424 of the Code) shall be not less than 110% of the Fair Market
Value of the Common Stock on the grant date and the term of such Option shall
not exceed five years.

         (g) OTHER TERMS AND CONDITIONS. Options may contain such other
provisions, not inconsistent with the provisions of the Plan, as the Committee
shall determine appropriate from time to time. No Option shall be an Incentive
Stock Option unless so designated by the Committee at the time of grant or in
the Grant Agreement evidencing such Option.

SECTION 7. RESTRICTED STOCK

         (a) GRANT BY COMPANY. The Board, upon recommendation of the Committee,
shall have authority to determine the Participants to whom Shares of Restricted
Stock (including Premium Shares, as defined below) shall be granted, the number
of Shares of Restricted Stock to be granted to each Participant, and the other
terms and conditions of such Awards.

         (b) PARTICIPANT ELECTION. Each Participant may elect Restricted Stock
in lieu of a portion of any annual cash bonus earned by such Participant up to
20% of such annual cash bonus. Such election is a one-time election to be made
annually during a Trading Window, as defined in the Company's Trading Policy,
with the right to amend the election in writing up to a maximum of two times per
fiscal year during Trading Windows only. Such Restricted Stock will vest ratably
over a period of years as determined by the Board. Such Restricted Stock may
have a premium in shares (the

<PAGE>

"Premium Shares") greater than the portion of the bonus to be paid in Restricted
Shares, as determined by the Board, which Premium Shares shall be delivered to
the Participant when the Award is fully vested, provided that the Participant is
in the employ of the Company when vesting occurs.

         (c) TRANSFER RESTRICTIONS. The Company shall deliver certificates for
Restricted Shares to the Participant or the Participant's legal representative
upon the lapse of all restrictions applicable to such shares of Restricted
Stock.

         (d) PAYMENT. Each share of Restricted Stock shall be paid in Shares,
upon the lapse of the restrictions applicable thereto, or otherwise in
accordance with the applicable Award Agreement.

         (e) RIGHTS OF OWNERSHIP. The Participant shall have all rights of
ownership to the Restricted Stock, including voting rights, dividends and other
distributions paid on or in respect of any Shares of Restricted Stock, except
for rights of transfer, which shall not exist until vesting has occurred.

SECTION 8. TERMINATION OF EMPLOYMENT.

         (a) In the event a Participant (other than a Non-Employee Director)
shall cease to be employed by the Corporation while he is holding one or more
Options, each outstanding Option which is exercisable on the date of such
termination shall expire at the earlier of the expiration of its term or one
year, unless the Board determines otherwise.

         Unless otherwise determined by the Board, any portion of an Option held
by a Participant (other than a Non-Employee Director) that is not exercisable on
the date such Participant's employment terminates shall expire as of such
termination date.

         (b) RESTRICTED STOCK. In the event of a Participant's retirement,
permanent and total disability, or death, or in cases of special circumstances,
the Board may, when it finds that a waiver would be in the best interest of the
Company, waive in whole or in part, any or all remaining restrictions with
respect to such Participant's entitlement to shares of Restricted Stock,
including any Premium Shares. In the event of a Participant's death while in the
employ of the Company, any or all remaining restrictions with respect to such
Participant's entitlement to shares of restricted stock shall be deemed waived
by the Board.

SECTION 9. TERMINATION OF SERVICE AS A DIRECTOR.

         (a) In the event a Director shall cease to serve as a Director of the
Corporation while he or she is holding one or more Options, each outstanding
Option which is exercisable as of the date of such termination shall expire at
the earlier of the expiration of its term or one year, unless the Board
determines otherwise.

         Unless otherwise determined by the Board, any portion of an Option held
by a Director which has not become exercisable as of the date a Director ceases
to serve as a Director of the Corporation shall terminate as of such date.

SECTION 10. CHANGE IN CONTROL.

Notwithstanding any other provision of the Plan to the contrary, upon a Change
in Control all outstanding Awards shall vest, become immediately exercisable or
payable and have all restrictions lifted as may apply to the type of Award.

SECTION 11. AMENDMENT AND TERMINATION.

         (a) AMENDMENTS TO THE PLAN. The Board may amend, alter, suspend,
discontinue, or terminate the Plan or any portion thereof at any time; provided
that no such amendment, alteration, suspension discontinuation or termination
shall be made without stockholder approval to: increase the number of shares
issuable; reduce the exercise price or otherwise reprice an Option, whether
previously granted or to be granted, or extend the termination period of the
Plan. The Board, however, may not amend or terminate the Plan without a
Participant's consent insofar as it would adversely affect a Participant's
rights to previously granted Awards.

<PAGE>

         (b) CANCELLATION. Any Award granted hereunder may be canceled with the
approval and agreement of the Participant in consideration of a cash payment or
alternative Award made to the holder of such canceled Award equal in value to
the Fair Market Value of such canceled Award.

SECTION 12. GENERAL PROVISIONS

         (a) NONTRANSFERABILITY. No Award shall be assigned, alienated, pledged,
attached, sold or otherwise transferred or encumbered by a Participant, except
by will or the laws of descent and distribution or pursuant to a QDRO.

         (b) NO RIGHTS TO AWARDS. No Participant or other Person shall have any
claim to be granted any Award, and there is no obligation for uniformity of
treatment of Participants, or holders or beneficiaries of Awards. The terms and
conditions of Awards need not be the same with respect to each recipient.

         (c) SHARE CERTIFICATES. All certificates for Shares or other securities
of the Company delivered under the Plan pursuant to any Award or the exercise
thereof shall be subject to such stop transfer orders and other restrictions as
the Board may deem advisable under the Plan or the rules, regulations, and other
requirements of the Securities and Exchange Commission, any stock exchange upon
which such Shares or other securities are then listed, and any applicable
Federal or state laws, and a legend or legends may be put on any such
certificates to make appropriate reference to such restrictions.

         (d) WITHHOLDING. A Participant may be required to pay to the Company
and the Company shall have the right and is hereby authorized to withhold from
any Award, from any payment due or transfer made under any Award or under the
Plan or from any compensation or other amount owing to a Participant the amount
(in cash, or Shares), of any applicable withholding taxes in respect of an
Award, its exercise, or any payment or transfer under an Award or under the Plan
and to take such other action as may be necessary in the opinion of the Company
to satisfy all obligations for the payment of such taxes.

         (e) AWARD AGREEMENTS. Each Award hereunder shall be evidenced by an
Award Agreement that shall be delivered to the Participant and shall specify the
terms and conditions of the Award and any rules applicable thereto.

         (f) NO RIGHT TO EMPLOYMENT. The grant of an Award shall not be
construed as giving a Participant the right to be retained in the employ of the
Company or any Affiliate. Further, the Company or an Affiliate may at any time
dismiss a Participant from employment, free from any liability or any claim
under the Plan, unless otherwise expressly provided in the Plan or in any Award
Agreement.

         (g) RIGHTS AS STOCKHOLDER. No holder of an Award of stock options or
beneficiary of any such Award shall have any rights as a stockholder with
respect to such options until he or she has exercised such option and become the
holder of Shares. In connection with each grant of Restricted Stock hereunder,
the applicable Award shall be entitled to the rights of a stockholder in respect
of such Restricted Stock, except for such transfer restrictions as may be
applicable thereto.

         (h) GOVERNING LAW. The validity, construction, and effect of the Plan
and any rules and regulations relating to the Plan and any Award Agreement shall
be determined in accordance with the laws of the State of New York.

         (i) SEVERABILITY. If any provision of the Plan or any Award is or
becomes or is deemed to be invalid, illegal, or unenforceable in any
jurisdiction or as to any Person or Award, or would disqualify the Plan or any
Award under any applicable law, such provision shall be construed or deemed
amended to conform to the applicable laws, or if it cannot be construed or
deemed amended without, in the determination of the Board, materially altering
the intent of the Plan or the Award, such provision shall be stricken as to such
jurisdiction, Person or Award and the remainder of the Plan and any such Award
shall remain in full force and effect.

<PAGE>

         (j) OTHER LAWS. The Company may refuse to issue or transfer any Shares
or other consideration under an Award if, it determines that the issuance or
transfer of such shares might violate any applicable law or regulation or
entitle the Company to recover the same under Section 16(b) of the Exchange Act,
and any payment tendered to the Company by a Participant, other holder or
beneficiary in connection with the exercise of such Award shall be promptly
refunded to the relevant Participant, holder, or beneficiary. Without limiting
the generality of the foregoing, no Award granted hereunder shall be construed
as an offer to sell securities of the Company, and no such offer shall be
outstanding, unless the Board has determined that any such offer, if made, would
be in compliance with all applicable requirements of the U.S. federal securities
laws any other laws to which such offer, if made, would be subject.

         (k) NO TRUST FUND CREATED. Neither the Plan nor any Award shall create
or be construed to create a trust or separate fund of any kind or a fiduciary
relationship between the Company and a Participant or any other Person. To the
extent that any Person acquires rights pursuant to an Award, such rights shall
be no greater than the rights of any unsecured general creditor of the Company.

         (l) NO OBLIGATION TO EXERCISE OPTIONS. The granting of an Option shall
impose no obligation upon the Participant to exercise such Option.

         (m) PLAN EXPENSES. Any expenses of administering this Plan shall be
borne by the Company.

         (n) NO WARRANTY OF TAX EFFECT. Except as may be contained in any Award
Agreement, no opinion shall be deemed to be expressed or warranties made as to
the effect of foreign, federal, state, or local tax on any Awards.

SECTION 13. RESTATEMENT OF SHARE OWNERSHIP GUIDELINES.

         (a) APPLICABILITY. The Board established the one-time Share ownership
guidelines in connection with its adoption of the Company's 1998 Omnibus Equity
Award Plan. These guidelines are restated in paragraph 13 (d) below. These
guidelines are applicable to the Chief Executive Officer of the Company ("CEO")
and to managerial Participants designated by the Board (together, "Designated
Participants").

         (b) MEASUREMENT. Share ownership guidelines are in terms of the Fair
Market Value of Shares to be owned relative to the positions held and the base
salaries of the Designated Participants. Ownership levels and guidelines will be
reviewed (and if advisable modified) by the Board (upon recommendation of the
Committee) periodically, based on internal reports and overall operations of the
Company.

         (c) TARGETED LEVELS. Designated Participants will either from inception
of the Company's 1998 Omnibus Equity Award Plan or commencement of employment
have five years to reach the targeted guideline levels of Share ownership set
forth in Paragraph 13 (d) below (except, that if a Designated Participant's Base
Salary is increased from under $100,000 to $100,000 or more, such Participant
will have only three years from the date of the increase in Base Salary to reach
the targeted guideline level of share ownership), which levels can be changed,
modified, or suspended by the Board. Restricted Stock awarded to a Participant
shall be included in calculating Shares owned.

         (d) GUIDELINES. The one-time share ownership guidelines are as follows:

                  (i)      The CEO shall at all times own Shares with a Fair
                           Market Value equal to two times his or her Base
                           Salary.

                  (ii)     All other Designated Participants with a Base Salary
                           of less than $100,000 shall at all times own Shares
                           with a Fair Market Value equal to one-half his or her
                           Base Salary.

                  (iii)    All other Designated Participants with a Base Salary
                           of $100,000 or more shall at all times own Shares
                           with a Fair Market Value equal to his or her Base
                           Salary.

<PAGE>

SECTION 14. EFFECTIVE DATE; TERMINATION DATE

         The Plan is effective as of September 5, 2002, the date on which the
Plan was adopted by the Board, subject to approval of the shareholders within
twelve months of such date. Unless previously terminated, the Plan shall
terminate on the close of business on September 5, 2012, ten years from its
effective date. Subject to other applicable provisions of the Plan, all Options
granted under the Plan prior to termination of the Plan shall remain in effect
until such Options have been satisfied or terminated in accordance with the Plan
and the terms of such Options.