<PAGE>

                                                                    EXHIBIT 10.1

                                PALL CORPORATION

                             1991 STOCK OPTION PLAN
                      (as amended effective April 17, 2002)


         Pall Corporation (the "Company"), in order to retain and attract
personnel for positions of responsibility with the Company and its subsidiaries
and to provide additional incentive to such personnel by offering them an
opportunity to obtain a proprietary interest in the Company, hereby authorizes
options to be granted to eligible employees (as hereinafter defined) of the
Company and its subsidiaries and to members of the Board of Directors of the
Company to purchase shares of Common Stock of the Company ("shares") upon the
terms and conditions described below in this Pall Corporation 1991 Stock Option
Plan (the "Plan")

         1. Administration of the Plan. The Plan shall be administered, and the
options under the Plan shall be granted, by the Compensation Committee of the
Company as from time to time constituted (the "Committee"). The Committee shall
consist of three members of the Board of Directors who are appointed by the
Board and are (i) "Non-Employee Directors" as defined in Rule 16b-3 of the
Securities and Exchange Commission under the Securities Exchange Act of 1934 or
any successor regulation, and (ii) "outside directors" as defined in the
regulations of the Internal Revenue Service under Section 162(m) of the Internal
Revenue Code. The members of the Committee shall serve, without compensation, at
the pleasure of the Board. Subject to the provisions of the Plan, the Committee
shall be authorized to interpret the Plan and the options granted under the
Plan, to establish, amend and rescind any rules and regulations relating to the
Plan, to determine the terms and provisions of the options described in Section
4 hereof, and to make all other decisions necessary or advisable for the
administration of the Plan. The Committee may correct any defect or supply any
omission or reconcile any inconsistency in the Plan or in any option in the
manner and to the extent the Committee deems desirable to carry it into effect.
Any decision of the Committee in the administration of the Plan, as described
herein, shall be final and conclusive. The Committee may act only by a majority
of its members in office, except that the members thereof may authorize any one
or more of their number or any officer of the Company to execute and deliver
documents on behalf of the Committee. No member of the Committee shall be liable
for anything done or omitted to be done by him or by any other member of the
Committee in connection with the Plan, except for his own willful misconduct or
as expressly provided by statute.

         2. Number of Shares Subject to Option. The aggregate number of shares
which may be issued under the Plan is one million five hundred thousand
(1,500,000) shares of Common Stock of the Company. Such shares may be either
authorized but unissued or reacquired shares. If after July 2, 1991 the Company
effects one or more stock splits, stock dividends, combinations, exchanges of
shares or similar capital adjustments, the number and kind of shares with
respect to which options may be granted under the Plan, the number and kind of
shares subject to each outstanding option and the option price per share under
each such option shall be proportionately and appropriately adjusted by the
Committee. If any option granted under the Plan, or any portion thereof, shall
expire or terminate for any reason without having been exercised in full, the
shares with respect to which it has not been exercised shall be available for
further options under the Plan.
<PAGE>

         With respect to incentive stock options granted after December 31, 1986
under this Plan and under all stock option plans of the Company and its parent
and subsidiary corporations, the aggregate fair market value (determined at the
time the option is granted) of the stock with respect to which such incentive
stock options are exercisable for the first time by the optionee during any
calendar year shall not exceed $100,000.

         3. Eligible Employees. Options may be granted only to officers and
other employees of the Company and of such other corporations as are subsidiary
corporations of the Company at the time of grant who, in the judgment of the
Committee, are in a position to contribute significantly to the Company's
success ("eligible employees") and to members of the Board of Directors of the
Company ("directors") except that no options shall be granted to members of the
Committee. The Committee is hereby given the authority to select the particular
eligible employees and directors (other than members of the Committee) to whom
options under the Plan are to be granted, to determine the number of shares to
be optioned to each such employee and director and to grant one or more options
under the Plan to any such employee or director from time to time, irrespective
of whether one or more options have been granted to such employee or director
under previous stock option plans of the Company. In exercising its authority
under the foregoing provisions of this Section 3, each member of the Committee,
as authorized by ss.717(a) of the New York Business Corporation Law, shall be
entitled to rely on information, opinions, reports and statements prepared or
presented by (i) one or more officers of the Company or any subsidiary of the
Company whom the member believes to be reliable and competent in the matters
presented or (ii) counsel, public accountants or other persons as to matters
which the member believes to be within such person's professional or expert
competence. Nothing in the Plan or in any option granted under the Plan shall
confer any rights (a) on any officer or other employee to continue in the employ
of the Company or any of its subsidiary corporations or shall interfere in any
way with the right of the Company or any of its subsidiary corporations, as the
case may be, to terminate his employment at any time or (b) on any director to
continue as a director.

         4. Terms of Options. Options granted under the Plan, irrespective of
the date of grant thereof, may be "incentive stock options" meeting the
requirements for such options prescribed by Section 422 of the Internal Revenue
Code of 1986, as amended (the "Code"), or may be options not so qualifying as
incentive stock options ("nonqualified options"). The determination as to
whether or not an option granted under the Plan shall be an incentive stock
option shall be made by the Committee except that all options granted to
directors who are not also employees of the Company or a subsidiary ("outside
directors") shall be nonqualified options; outside directors shall not be
eligible to receive incentive stock options.

         Each option granted under the Plan shall comply with the following
terms and conditions:

                  (a) The option price shall be not less than the fair market
         value of the shares subject to the option at the time the option is
         granted. Fair market value shall be as determined in good faith by the
         Committee. In no event shall the option price be less than the par
         value of the shares.

                                       2
<PAGE>

                  (b) The option shall not be transferable by the optionee
         otherwise than by will or the laws of descent and distribution, and
         shall be exercisable during his or her lifetime only by him or her
         except that, at the discretion of the Committee, a nonqualified option
         may provide that the option is transferable to any "family member" of
         the optionee, as the term "family member" is defined in the General
         Instructions to Form S-8 promulgated by the Securities and Exchange
         Commission under the Securities Act of 1933.

                  (c)      An option shall not be exercisable

                           (i) after the expiration of ten years from the date
                  it is granted (the "date of grant");

                           (ii) unless counsel for the Company shall be
                  satisfied that the issuance of shares upon exercise will be in
                  compliance with the Securities Act of 1933, as amended, and
                  applicable state laws;

                           (iii) unless written notice of exercise, in form
                  satisfactory to the Committee, is given to the Company;

                           (iv) unless the optionee has been, at all times
                  during the period beginning with the date of grant of an
                  option and ending on the date of exercise thereof: (I) an
                  officer or employee of the Company or of one of its subsidiary
                  corporations, or of a corporation or a parent or subsidiary of
                  a corporation assuming the option in a transaction to which
                  Section 424(a) of the Code applies or (II) an outside director
                  if the optionee was an outside director on the date of grant,
                  except that

                                    (A) if the optionee shall cease to be such
                           an officer or employee or outside director by reason
                           of his disability or by reason of his retirement
                           under an approved retirement program of the Company
                           or a subsidiary thereof while holding an option which
                           has not expired and has not been fully exercised, the
                           option shall remain in full force and effect and may
                           be exercised in accordance with its terms until it
                           expires by its terms by the passage of time or is
                           canceled or terminated in accordance with its terms
                           (it being understood, however, that incentive stock
                           option federal income tax treatment will not be
                           accorded with respect to an option exercise made more
                           than three months after the optionee ceased to be
                           such officer or employee by reason of such retirement
                           or one year after he ceased to be such officer or
                           employee by reason of disability within the meaning
                           of Section 22(e)(3) of the Code or successor
                           section); and

                                    (B) if any person to whom an option has been
                           granted shall die holding an option which has not
                           been fully exercised, his estate or any person who
                           acquired the right to exercise the option by bequest
                           or inheritance or by reason of the death of such
                           person may, at any time within one year after the
                           date of such death (but in no event after the option
                           has expired by its terms by the passage of time or
                           has been canceled or terminated in accordance with
                           its terms) exercise the option with respect to any
                           shares as to which the decedent could have exercised
                           the option at the time of his death; and

                                       3
<PAGE>

                                    (C) if the optionee shall cease to be an
                           employee for any reason other than disability,
                           retirement or death as provided in paragraphs (A) and
                           (B) of this Section 4(a)(iv), while holding an option
                           which has not expired and has not been fully
                           exercised, the Committee may, in its sole discretion,
                           amend the option to permit its exercise at any time
                           within six months (or such shorter period as the
                           Committee may specify) after the date on which the
                           optionee ceases to be an employee (but in no event
                           after the option has expired by its terms by the
                           passage of time or has been canceled or terminated in
                           accordance with its terms), provided that (I) any
                           optionee who exercises an option under this paragraph
                           (C) after he or she ceases to be an employee may not
                           elect to pay the "purchase price" on an installment
                           basis as provided in Section 4(d) hereof, and (II) it
                           is understood that incentive stock option federal
                           income tax treatment will not be accorded with
                           respect to an option exercise made, in accordance
                           with action by the Committee pursuant to this
                           paragraph, more than three months after the optionee
                           ceased to be an employee; and

                           (v) unless the person exercising the option makes
                  payment to the Company in full in United States dollars by
                  cash or check of such amount as is sufficient to satisfy the
                  Company's obligation, if any, to withhold federal, state and
                  local taxes by reason of such exercise or makes such other
                  arrangement satisfactory to the Committee as will enable the
                  Company to satisfy such obligation.

                  (d) Each option granted under the Plan shall be evidenced by
         an instrument in such form as the Committee shall prescribe from time
         to time in accordance with the Plan and all applicable laws and
         regulations and shall be subject to such terms and conditions relating
         to the time at which the option may first be exercised and the number
         of shares with respect to which it may thereafter be exercised from
         time to time (for example, in cumulative annual or other periodic
         installments), and to such additional terms and conditions not
         inconsistent with the Plan or applicable laws and regulations, as the
         Committee may in its discretion determine. Each nonqualified option
         granted under the Plan shall state that it is not to be treated as an
         incentive stock option. Each option granted under the Plan shall
         require that the person exercising the option shall, at the time notice
         of exercise is given pursuant to Section 4(c)(iii) hereof, make full
         payment in United States dollars by cash or check of the option
         exercise price of the shares being acquired except that, at the
         election of the Committee, an option may provide that, at the time
         notice of exercise is given pursuant to section 4(c)(iii) hereof, the
         person exercising the option, at his or her election, shall either make
         full payment in United States dollars by cash or check of the option
         exercise price of the shares being acquired (sometimes hereafter called
         the "purchase price") or agree to pay such purchase price on an
         installment payment basis on the following terms and conditions:

                                       4
<PAGE>

                                    (A) The installments payable shall be the
                           minimum amounts required to be paid by Regulation U
                           of the Board of Governors of the Federal Reserve
                           System as in effect as of the date of exercise of the
                           option (hereinafter "Regulation U") or such greater
                           installment payments as the Committee may prescribe.

                                    (B) The person exercising the option shall
                           not be required to pay interest to the Company on the
                           unpaid balance of the purchase price.

                                    (C) The unpaid balance of the purchase price
                           shall be immediately payable in full upon demand made
                           by the Company to the optionee (or to the successor
                           owner of the stock if the optionee has died).

                                    (D) The shares for which the option is
                           exercised shall be issued to and registered in the
                           name of the person exercising the option but shall be
                           endorsed by the person exercising the option in blank
                           (either on the certificate or on a separate stock
                           power) and held by the Company as collateral security
                           for the unpaid balance of the purchase price. The
                           person exercising the option shall not be permitted
                           to sell, withdraw, pledge or otherwise dispose of all
                           or any part of such collateral except at a time when
                           such sale, withdrawal, pledge or other disposition is
                           permitted by Regulation U. Subject to compliance with
                           the immediately preceding sentence, the person
                           exercising the option shall have the right at any
                           time and from time to time to withdraw part or all of
                           the shares from the collateral so held by the Company
                           upon payment of the unpaid balance of the purchase
                           price of the shares withdrawn. For purposes of
                           determining such unpaid balance, each payment made
                           otherwise than to obtain withdrawal of shares under
                           the immediately preceding sentence shall be applied
                           pro rata to all shares which at the time of such
                           payment are held by the Company as collateral for the
                           payment of the purchase price by the person
                           exercising the option. Upon default by the person
                           exercising the option in the making of any payment
                           due under the foregoing provisions of this
                           subparagraph (d), the Company shall have with respect
                           to the collateral all of the rights of a secured
                           party under the Uniform Commercial Code as in effect
                           in the State of New York.

                                    (E) The person exercising an option shall be
                           entitled, from the date of exercise of such option,
                           to all of the rights of a shareholder, including the
                           right to vote the shares and to receive and retain
                           all dividends paid thereon.

                                       5
<PAGE>

                  (e) The Committee is authorized in its discretion and with the
         consent of the optionee to make amendments, not in conflict with the
         Plan or any applicable law or regulation, in the terms of any option
         granted under the Plan.

                  (f) In addition to the methods of payment of the option
         exercise price authorized by subparagraph (d) next above, the option
         may provide that the person exercising the option, at his or her
         election, shall have the right to make payment at the time of exercise
         by delivering to the Company shares of Common Stock of the Company
         having a total fair market value equal to the option exercise price, or
         a combination of cash and such shares having a total fair market value
         equal to the option exercise price, provided, however, that all shares
         so delivered must have been beneficially owned by the person exercising
         the option for at least six months prior to the option exercise date
         and, upon request, the Company shall be given satisfactory proof of
         such beneficial ownership. For the purposes of the preceding sentence,
         the fair market value of a share of Common Stock shall be the mean
         between the high and low sale prices of the Common Stock on the trading
         day preceding the option exercise date as such prices are reported by
         and for the New York Stock Exchange, Inc. Composite Transactions.
         Certificates representing shares delivered to the Company pursuant to
         this paragraph shall be duly endorsed or accompanied by appropriate
         stock powers, in either case with signature guaranteed if so required
         by the Company.

         5. Interpretation. The words "employee", "own", "outstanding" and
"disposition", the term "subsidiary corporation" and any other words or terms
used in the Plan or in the options granted under the Plan which are defined or
used in Section 422 or 424 of the Code shall, unless the context clearly
requires otherwise, have the meanings assigned to them therein, irrespective of
whether or not such options are incentive stock options.

         6. Reports and Returns. The appropriate officers of the company shall
cause to be filed, or furnished to all employees to whom options have been
granted, any reports, returns or other information regarding the options granted
hereunder or any shares issued pursuant to the exercise thereof as may be
required by the Code, the Securities Act of 1933, the Securities Exchange Act of
1934, the Employee Retirement Income Security Act of 1974, Regulation U of the
Board of Governors of the Federal Reserve System or any other applicable
statute, rule or regulation, as any such statute, rule or regulation has been
amended to the time in question.

         7. Amendment. The Plan may be amended at any time and from time to time
by the Board of Directors of the Company, but no amendment increasing the
aggregate number of shares which may be issued under options granted pursuant to
the Plan or affecting this sentence shall be effective unless the same be
approved by the shareholders of the Company not later than the date 12 months
after the Board adopts the amendment. No amendment of the Plan shall alter or
impair any of the rights or obligations of any person, without his or her
consent, under any option theretofore granted under the Plan.

                                       6
<PAGE>

         8. Termination. The Plan shall terminate upon the earlier of the
following dates or events to occur:

                  (a) upon the adoption of a resolution of the Board of
Directors of the Company terminating the Plan; or

                  (b) July 1, 2001.

         No termination of the Plan shall alter or impair any of the rights or
obligations of any person, without his or her consent, under any option
theretofore granted under the Plan.

         9. Shareholder Approval. The Plan shall be submitted to the
shareholders of the Company for their approval before July 2, 1992. No option
granted hereunder shall be exercisable until such approval has been obtained. If
the shareholders do not approve the Plan before July 2, 1992, the Plan shall
terminate and all options theretofore granted hereunder shall thereupon be void
without further action of the Company. The shareholders shall be deemed to have
approved the Plan only if it is approved at a meeting of the shareholders duly
held before July 2, 1992, by vote taken in the manner required by the laws of
the State of New York.


As adopted by the Board of Directors of
Pall Corporation on July 2, 1991, approved
by the shareholders at the annual meeting
on November 22, 1991, amended by the
Executive Committee on November 19, 1998,
and amended by the Board of Directors on
April 17, 2002.


                                       7