Document:

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                                                                     EXHIBIT 4.2

                                   [Wilson Sonsini Goodrich & Rosati Letterhead]

                                   October 11, 2000

[Selling Stockholder Address]

        RE: AUSPEX SYSTEMS, INC. - SHARE PURCHASE AGREEMENT

Dear [Selling Stockholder]:

        Auspex Systems, Inc., (the "Company"), is requesting that you amend the
Share Purchase Agreement dated September 19, 2000. As you are aware, the Company
engaged Halpern Capital Management, Inc. ("Halpern") as a placement agent in the
recent private placement of the Company's Common Stock. The Company would like
to pay part of the placement fee to Halpern in the form of a warrant to purchase
566,048 shares of Common Stock. The exercise price per share of the warrant will
be $7.9625, which is the price that you paid for your shares under the Share
Purchase Agreement.

        The terms of the Share Purchase Agreement prohibit the Company from
including the shares subject to this warrant in the registration statement on
Form S-3. The Company is requesting that you amend Sections 7.1.1(j) and (k) to
state as follows:

        7.      Form D Filing; Registration; Compliance with the Securities Act;
                Covenants.

                7.1     Form D Filing; Registration of Shares.

                        7.1.1   Registration Statement; Expenses.

        The Company, which as of the date of Closing is eligible to use a Form
        S-3 registration statement, shall: . . .

                (j)     not allow any shareholders other than the Purchasers and
                        Baruch Halpern and Shoshana Halpern, to include their
                        shares in the Registration Statement;

                (k)     not file another registration statement or make any
                        other offers of securities, either of which would cause
                        the offering of the Shares to be integrated with any
                        other securities offering of the Company, except that
                        the Company may file any registration statement required
                        pursuant to that certain Registration Rights Agreement
                        between the Company and certain buyers dated January 18,
                        2000 and may issue shares pursuant to conversion of the
                        Series B Preferred Stock and pursuant to a warrant and a
                        warrant purchase agreement with Baruch Halpern and
                        Shoshana Halpern;

<PAGE>   2

October 11, 2000
Page 2

        In addition, the Company would like to amend the Representations,
Warranties and Covenants Section of the Share Purchase Agreement with respect to
the capitalization of the Company as follows:

                4.2     Capitalization . . .

                        (d)     The Company has reserved 1,605,136 shares of
                                Common Stock for issuance upon the exercise of
                                outstanding warrants to purchase Common Stock
                                and the Company expects to reserve 566,048
                                shares of Common Stock for exercise of warrants
                                that the Company anticipates issuing to the
                                placement agent.

        If you agree to amend the Share Purchase Agreement as stated above,
please sign and date this letter as noted below and return it to the undersigned
by facsimile at (650) 461-5375.

        Please call Gina Christopher at Wilson Sonsini Goodrich and Rosati at
(650) 565-3540 if you have any questions about this letter.

                                       Sincerely,

                                       WILSON SONSINI GOODRICH & ROSATI
                                       Professional Corporation

                                       /s/ Gina M. Christopher

                                       Gina M. Christopher

        I hereby agree to amend the Share Purchase Agreement as described above.

        Shareholder:     State of Wisconsin
                         ------------------------------------------

        By:              /s/ John F. Nelson
                         ------------------------------------------

        Name:            John F. Nelson
                         ------------------------------------------

        Title:           Investment Director
                         ------------------------------------------

        # of shares:     2,750,000
                         ------------------------------------------

        Date:            10/12/2000
                         ------------------------------------------

<PAGE>   3

October 11, 2000
Page 3

        Shareholder:     CastleRock Partners, L.P.
                         ------------------------------------------

        By:              /s/ Paul P. Tanico
                         ------------------------------------------

        Name:            Paul P. Tanico
                         ------------------------------------------

        Title:           Management Member of the General Partner
                         ------------------------------------------

        # of shares:     326,531
                         ------------------------------------------

        Date:            10/12/2000
                         ------------------------------------------

        Shareholder:     CastleRock Fund, Ltd.
                         ------------------------------------------

        By:              /s/ Paul P. Tanico
                         ------------------------------------------

        Name:            Paul P. Tanico
                         ------------------------------------------

        Title:           Principal of the Investment Advisor
                         ------------------------------------------

        # of shares:     145,683
                         ------------------------------------------

        Date:            10/12/2000
                         ------------------------------------------

        Shareholder:     CastleRock Partners II, L.P.
                         ------------------------------------------

        By:              /s/ Paul P. Tanico
                         ------------------------------------------

        Name:            Paul P. Tanico
                         ------------------------------------------

        Title:           Managing Member of the General Partner
                         ------------------------------------------

        # of shares:     30,141
                         ------------------------------------------

        Date:            10/12/2000
                         ------------------------------------------

<PAGE>   4

October 11, 2000
Page 4

                         Franklin Strategic Series
                         On behalf of Franklin Small Cap Growth
        Shareholder:     Fund I
                         ------------------------------------------

        By:              /s/ David P. Goss
                         ------------------------------------------

        Name:            David P. Goss
                         ------------------------------------------

        Title:           Vice President
                         ------------------------------------------

        # of shares:     1,255,887
                         ------------------------------------------

        Date:            10/13/2000
                         ------------------------------------------

        Shareholder:     Franklin Templeton Variable Insurance
                         Products Trust
                         On behalf of Franklin Small Cap Growth
                         Fund
                         ------------------------------------------

        By:              /s/ David P. Goss
                         ------------------------------------------

        Name:            David P. Goss
                         ------------------------------------------

        Title:           Vice President
                         ------------------------------------------

        # of shares:     1,255,887
                         ------------------------------------------

        Date:            10/13/2000
                         ------------------------------------------<PAGE>   1
                                                                     EXHIBIT 4.1

                                  ABAXIS, INC.

                        SECURITIES SUBSCRIPTION AGREEMENT

     THIS SECURITIES SUBSCRIPTION AGREEMENT (the "Agreement") is made as of
October 4, 2000, between Abaxis, Inc., a California corporation ("Seller") and
the subscribers listed on the Schedule of Subscribers attached hereto as
Schedule I (a "Subscriber" or collectively, the "Subscribers"). Each Subscriber
hereby represents and warrants to, and agrees with Seller as follows:

     1.   Agreement to Subscribe; Subscription Price.

          (a)  Number of Shares; Purchase Price. Subscribers hereby agree to
purchase from Seller up to 10,000 shares of its Series D Preferred Stock (the
"Shares") at a purchase price of $1000 per share (the "Purchase Price"). The
rights, restrictions, privileges and preferences of the Shares are as set forth
in the Certificate of Determination of Rights, Restrictions (the "Certificate of
Determination") attached hereto as Exhibit A.

          (b)  Sale and Issuance of the Shares. Subject to the terms and
conditions hereof, at the Closing Date (as defined below), Seller will issue and
sell to each Subscriber and each Subscriber agrees, severally and not jointly,
to subscribe from Seller that number of the Shares set forth opposite each
Subscriber's name on Schedule I. Subscribers shall pay the Purchase Price by
delivering good funds in United States Dollars to the Escrow Agent (as defined
below) for closing by delivery of securities versus payment on October 4, 2000
or at such time as is mutually acceptable to both parties (the "Closing Date").

          (c)  Issuance of Warrants. In consideration of the subscription of the
Shares, Seller agrees to issue to each Subscriber, a warrant to purchase the
number of shares of the Seller's Common Stock equal to five percent (5%) of the
amount of the Purchase Price paid by such Subscriber divided by $7.00, such
warrant to be substantially in the form attached hereto as Exhibit B (the
"Warrants").

          (d)  Conditions to Obligations of Seller. Seller's obligation to sell
the Shares and to issue the Warrants to a Subscriber is conditioned upon the
following:

               (i)  The receipt and acceptance by Seller of this Agreement for
the sale of the Shares and the issuance of the Warrants, as evidenced by the
execution of this Agreement by authorized officers of Subscriber.

               (ii) The delivery to the Escrow Agent by each Subscriber of good
funds in the amount of the Purchase Price for the Shares.

               (iii) The Certificate of Determination shall have been filed
with, and accepted by, the Secretary of State of the State of California.

<PAGE>   2

          (e)  Conditions to Obligations of Subscriber. Subscriber's obligation
to purchase the Shares from Seller is conditioned upon the following:

               (i)  The receipt and acceptance by Subscribers of this Agreement
for the purchase of the Shares, as evidenced by the execution of this Agreement
by authorized officers of Seller.

               (ii) The delivery to the Escrow Agent by Seller of one or more
stock certificates of Seller representing, in aggregate, the number of Shares
purchased by each of the Subscribers and conforming in all material respects to
the requirements of this Agreement.

               (iii) The delivery at Closing of a certificate from an authorized
officer of Seller certifying that Seller's representations and warranties
hereunder are true and correct as of the closing date.

               (iv) The Certificate of Determination shall have been filed with,
and accepted by, the Secretary of State of the State of California.

          (f)  Deliveries. The Purchase Price for the Shares will be directed to
the Trust Account of Gray Cary Ware & Freidenrich LLP (Account #6470017579),
Attn: Andrew Zeif, Esq., as Escrow Agent, Union Bank of California, 400
University Avenue, Palo Alto, CA 94301, ABA #122000496, on or before the Closing
Date. The subscription price for the Shares will, upon deposit into and
collection for the above account, be delivered to Seller by certified check or
by wire transfer, subject to prior delivery to said Escrow Agent of certificates
representing the purchased Shares in accordance with the terms of this
Agreement. Upon execution of said transfer, the Escrow Agent shall deliver the
certificates representing the purchased Shares to the Subscriber in accordance
with the Subscriber's instructions.

          (g)  Indemnification of Escrow Agent. Seller and Subscriber each
agrees, jointly and severally, to indemnify and hold harmless the Escrow Agent
from any and all claims, liabilities, losses, actions, suits, or proceedings, at
law or in equity, that it may incur by reason of its acting as escrow agent as
described herein (including but not limited to expenses reasonably incurred in
investigating, preparing or defending against any litigation, commenced);
provided, however, that the provisions of this paragraph shall not apply in the
event of any claim, liability, loss, action, suit, of proceeding resulting from
the gross negligence or willful misconduct of the Escrow Agent.

     2.   Subscriber Representations, Access to Information; Independent
Investigation.

          Each Subscriber severally and not jointly, represents and warrants to
Seller as follows:

          (a)  Subscriber's Qualifications. Subscriber

               (i)  is an "accredited investor" within the meaning of Securities
and Exchange Commission ("SEC") Rule 501 of Regulation D, as presently in
effect;

                                       2

<PAGE>   3

               (ii) has the full right, power and authority to enter into this
Agreement and to carry out and consummate the transactions contemplated herein
and this Agreement constitutes the legal, valid and binding obligation of
Subscriber;

               (iii) is purchasing the Shares and the Warrants initially for its
own account, for investment purposes only and not with the view towards
distribution or reselling of such Shares and the Warrants or any part thereof;

               (iv) has a preexisting personal or business relationship with
Seller and/or certain of its officers and/or directors of a nature and duration
sufficient to make Subscriber aware of the character, business acumen and
general business and financial circumstances of Seller and/or such officers and
directors. By reason of Subscriber's business or financial experience,
Subscriber is capable of evaluating the merits and risks of this investment, has
the ability to protect Subscriber's own interests in this transaction and is
financially capable of bearing a total loss of this investment; and

               (v)  Subscriber understands that (i) the Shares and the Warrants
are being offered and sold to it in reliance on specific exemptions from the
registration requirements of United States federal and state securities laws,
(ii) the Shares and the Warrants have not been registered with any United States
federal or state securities commissions and (iii) Seller is relying upon the
truth and accuracy of the representations, warranties, agreements,
acknowledgments and understandings of Subscriber set forth herein in order to
determine the applicability of such exemptions and the suitability of Subscriber
to acquire the Shares and the Warrants.

          (b)  Public Information Subscriber has received copies of the Seller's
most recent Annual Report on Form 10-K filed with the Securities and Exchange
Commission and all Quarterly Reports on Form 10-Q and all Current Reports on
Form 8-K filed thereafter (collectively the "SEC Filings"), and other publicly
available documents and has carefully reviewed these SEC Filings.

          (c)  Legal Compliance. Subscriber has satisfied itself as to the full
observance of the laws of its jurisdiction in connection with any invitation to
subscribe for the Shares and the Warrants or any use of this Agreement,
including (i) the legal requirements within its jurisdiction for the purchase of
the Shares and the Warrants, (ii) any foreign exchange restrictions applicable
to such purchase, (iii) any governmental or other consents that may need to be
obtained and (iv) the income tax and other tax consequences, if any, that may be
relevant to the purchase, holding, redemption, sale, or transfer of the Shares
and the Warrants. Subscriber's subscription and payment for, and its continued
ownership of the Shares and the Warrants, will not violate any applicable
securities or other laws of its jurisdiction.

          (d)  Due Diligence. Subscriber and its representatives have been
solely responsible for Subscriber's own "due diligence" investigation of Seller
and its management and business, for its own analysis of the merits and risks of
this investment, and for its own analysis of the fairness and desirability of
the terms of the investment. In taking any action or performing any role
relative to the arranging of the proposed investment, Subscriber has acted
solely in its own interest, and neither Subscriber nor any of its
representatives has acted as an agent of Seller.

                                       3

<PAGE>   4

          (e)  No Consents or Approvals. No consent, approval or authorization
of or designation, declaration or filing with any governmental authority on the
part of Subscriber is required in connection with the valid execution, delivery
and performance of this Agreement.

     3.   Seller Representations.

          (a)  Rights, Preferences, Privileges and Restrictions. The rights,
preferences, privileges and restrictions of the Shares are substantially as set
forth in the Certificate of Determination or in this Agreement.

          (b)  Legal Compliance. Seller is in compliance, to the extent
applicable, with all reporting obligations under either Section 12(b), 12(g) or
15(d) of the Securities Exchange Act of 1934, as amended (the "Exchange Act").
Seller has registered its Common Stock pursuant to Section 12 of the Exchange
Act and the Common Stock trades on the Nasdaq National Market System.

          (c)  Concerning the Shares. The Shares and additional shares of Common
Stock issuable upon exercise of the Warrants when issued and delivered hereunder
will be duly and validly authorized and issued, fully paid and non-assessable
and free from preemptive rights.

          (d)  Subscription Agreement. This Agreement has been duly authorized,
validly executed and delivered on behalf of the Seller and is a valid and
binding agreement in accordance with its terms, subject to general principles of
equity and to bankruptcy or other laws affecting the enforcement of creditors'
rights generally.

          (e)  Non-Contravention. The execution and delivery of this Agreement
and the consummation of the issuance of the Shares and the transactions
contemplated by this Agreement do not and will not conflict with or result in a
material breach by Seller of any of the terms or provisions of, or constituent
default under, the articles of incorporation or by-laws of Seller, or any
indenture, mortgage, deed of trust or other material agreement or instrument to
which Seller is a party or by which it or any of its properties or assets are
bound, or any existing applicable law, rule or regulation or any applicable
decree, judgment or order of any court, United States federal or state
regulatory body, administrative agency or other governmental body having
jurisdiction over Seller or any of its properties or assets.

          (f)  Approvals. Seller is not aware of any authorization, approval or
consent of any governmental body which is legally required for the issuance and
sale of the Shares and the Warrants as contemplated by this Agreement.

     4.   Restrictive Legend.

          (a)  The Shares and the Warrants have been issued with the following
legend (the "Legend") appearing thereon:

          Federal Legend. THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT
          BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,

                                       4
<PAGE>   5

          AS AMENDED, AND MAY NOT BE SOLD, TRANSFERRED, ASSIGNED OR HYPOTHECATED
          UNLESS THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT
          COVERING SUCH SECURITIES, THE TRANSFER IS MADE IN COMPLIANCE WITH RULE
          144 PROMULGATED UNDER SUCH ACT OR THE SELLER RECEIVES AN OPINION OF
          COUNSEL FOR THE HOLDER OF THESE SECURITIES REASONABLY SATISFACTORY TO
          THE SELLER, STATING THAT SUCH SALE, TRANSFER, ASSIGNMENT OR
          HYPOTHECATION IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY
          REQUIREMENTS OF SUCH ACT.

          (b)  Transferability. Seller need not register a transfer of any
Shares, and may also instruct its transfer agent not to register the transfer of
the Shares.

     5.   Registration Rights.

          (a)  Registration. As soon as practicable after the Closing Date, and
not more than forty-five (45) days thereafter, Seller shall file a registration
statement on Form S-3 (or any successor form) with respect to shares of Abaxis
Common Stock issuable upon conversion of the Shares or exercise of Warrants
(such registration statement and any successor or substitute registration
statement is herein referred to as the "Registration Statement"). Seller shall
use its best efforts to cause such Registration Statement to become effective as
promptly as practicable and to maintain the effectiveness of the Registration
Statement (and to maintain the current status of the prospectus contained
therein) until the earlier of (i) the date one year from the Closing Date or
(ii) when all the Shares have been resold pursuant to an effective Registration
Statement. It shall be a condition precedent to the right of any Subscriber to
sell Shares under the Registration Statement and the obligation of Seller to
file the Registration Statement that such Subscriber shall have furnished to
Seller such information regarding itself, the Shares held by it, the intended
method of distribution of such securities and any additional information as
shall be required to be included in the Registration Statement with respect to
such Shares. Seller shall provide each Subscriber with a copy of each
Registration Statement, each amendment or supplement thereto, and the prospectus
contained therein (as amended and/or supplemented).

     6.   Miscellaneous.

          (a)  Entire Agreement. Except as specifically referenced herein, this
Agreement constitutes the entire contract between the parties, and neither party
shall be liable or bound to the other in any manner by any warranties,
representations or covenants except as specifically set forth herein. Any
previous agreement among the parties related to the transactions described
herein is superseded hereby. The terms and conditions of this Agreement shall
inure to the benefit of and be binding upon the respective successors and
assigns of the parties hereto. Nothing in this Agreement, express or implied, is
intended to confer upon any party, other than the parties hereto, and their
respective successors and assigns, any rights, remedies, obligations or
liabilities under or by reason of this Agreement, except as expressly provided
herein.

                                       5
<PAGE>   6

          (b)  Governing Law. This Agreement shall be governed by, and
interpreted in all respects by, the laws of the State of California as such laws
are applied to agreements between California residents entered into and to be
performed entirely within California.

          (c)  Survival. The representations, warranties, covenants and
agreements made herein shall survive the execution of this Agreement and the
closing of the transactions contemplated hereby.

          (d)  No Brokers. Subscriber (i) represents and warrants to the Seller
that it has retained no finder or broker in connection with the transactions
contemplated by this Agreement and (ii) hereby agrees to indemnify and to hold
Seller harmless of and from any liability for any commission or compensation in
the nature of a finder's fee to any broker or other person of firm (and the
costs and expenses of defending against such liability or asserted liability)
for which it, or any of its employees or representatives, are responsible.

          (e)  Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

                                       6
<PAGE>   7

     IN WITNESS WHEREOF, the parties hereto have caused this Offshore Securities
Subscription Agreement to become effective this 4th day of October, 2000.

ABAXIS, INC.

By: /s/ Donald Stewart
    ------------------
    Donald Stewart
    Vice President, Finance and
    Chief Financial Officer

SUBSCRIBER

By:
   ----------------------------
Name:
     --------------------------
Title:
      -------------------------

                                       7
<PAGE>   8
                                   SCHEDULE I

                             SCHEDULE OF SUBSCRIBERS

<TABLE>
<CAPTION>
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Name and Address of Subscriber           Number of Shares           Warrants         Purchase Price
---------------------------------------------------------------------------------------------------
<S>                                     <C>                        <C>               <C>
---------------------------------------------------------------------------------------------------

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          Total
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</TABLE>

                                       8
<PAGE>   9

                                    EXHIBIT A

                          CERTIFICATE OF DETERMINATION

9
<PAGE>   10

                                   EXHIBIT B

                                 FORM OF WARRANT

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