Document:

<PAGE>   1
                                                                   Exhibit 10.21

                               FIRST AMENDMENT TO
                         COMMON STOCK PURCHASE AGREEMENT

         This FIRST AMENDMENT to COMMON STOCK PURCHASE AGREEMENT (this
"Amendment") is made and entered into this ___ day of October 2000, by and
between BECKMAN COULTER, INC. ("Beckman") and CELLOMICS, INC. (the "Company").

                                   WITNESSETH

         WHEREAS, Beckman and the Company have entered into a certain Common
Stock Purchase Agreement dated June 9, 2000 (the "Purchase Agreement") whereby
Beckman purchased 153,256 shares of the Company's Common Stock; and

         WHEREAS, Beckman and the Company wish to amend certain provisions of
the Purchase Agreement.

         NOW, THEREFORE, intending to be legally bound hereby, the parties
hereto amend the Purchase Agreement and agree as follows:

         1. COMMON STOCK. Beckman and the Company agree that the definition of
         Common Stock, as such term is used in the Purchase Agreement, shall be
         deleted in its entirety and replaced with the following:

                  Common Stock shall mean the Company's authorized Eight Million
                  (8,000,000) shares of Common Stock, par value $.01 per share.

         2. PREFERRED STOCK. Beckman and the Company agree that the definition
         of Preferred Stock, as such term is used in the Purchase Agreement,
         shall be deleted in its entirety and replaced with the following:

                  Preferred Stock shall mean the Company's authorized Four
                  Million Three Hundred Seventy-Four Thousand Five Hundred
                  (4,374,500) shares of Preferred Stock, par value $.01 per
                  share.

         3. REPRESENTATIONS AND WARRANTIES. Except as is otherwise modified,
         amended and/or restated in this Section 3, the representations and
         warranties of the Company as are set forth in Section 5.1 of the
         Purchase Agreement shall be true and correct in all material respects
         as of the date of this Amendment.

                  a. ORGANIZATION AND STANDING; ARTICLES AND BYLAWS. Section 3.1
         of the Purchase Agreement is hereby amended in order to attach, as
         Exhibit A, the Company's Amended and Restated Certificate of
         Incorporation (the "Restated Certificate") as presently in effect on
         the date hereof.

                  b. CAPITALIZATION. Section 3.3 of the Purchase Agreement is
         hereby deleted in its entirety and replaced with the following:

<PAGE>   2

                  As of the date of this Amendment, the Company's authorized
                  capital stock consists of (a) Eight Million (8,000,000) shares
                  of Common Stock, par value $.01 per share of the Company (the
                  "Common Stock"), of which One Million Three Hundred
                  Thirty-Eight Thousand Five Hundred Seventy-Five (1,338,575)
                  shares are issued and outstanding, and (b) Four Million Three
                  Hundred Seventy-Four Thousand Five Hundred (4,374,500) shares
                  of Preferred Stock, par value $.01 per share of the Company
                  ("Preferred Stock"), of which (i) Two Million Twenty-Four
                  Thousand Five Hundred (2,024,500) shares have been designated
                  Series A Preferred Stock, par value $.01 per share of the
                  Company (the "Series A Preferred"), of which One Million Nine
                  Hundred Sixty-Six Thousand Six Hundred Eighteen (1,966,618)
                  shares are issued and outstanding, (ii) Seven Hundred Thousand
                  (700,000) shares have been designated Series B Preferred
                  Stock, par value $.01 per share of the Company (the "Series B
                  Preferred"), of which Six Hundred Ninety-Three Thousand Six
                  Hundred Seventy-Five (693,675) shares are issued and
                  outstanding, and (iii) One Million Six Hundred Fifty Thousand
                  (1,650,000) shares have been designated as Series C Preferred
                  Stock, par value $.01 per share of the Company (the "Series C
                  Preferred"), of which One Million Six Hundred Forty-Five
                  Thousand Six Hundred Thirty-Nine(1,645,639) are issued and
                  outstanding. The Company has (i) issued warrants exercisable
                  for 388,141 and 57,829 shares of Common Stock and Preferred
                  Stock, respectively and (ii) reserved 742,900 shares of Common
                  Stock for issuance under its stock incentive plans, duly
                  adopted by the Board of Directors and approved by the
                  Company's stockholders of which options to purchase 493,057
                  shares of Common Stock have been granted. Upon consummation of
                  the Closing, all issued and outstanding shares of capital
                  stock of the Company will have been duly authorized and
                  validly issued, will be fully paid and nonassessable and will
                  have been issued in compliance with all applicable federal and
                  state securities laws. The Company holds no shares of its
                  capital stock in its treasury.

                  In the event of a sale of New Securities (as such term is
                  defined in that certain Amended and Restated Shareholders'
                  Agreement dated September 27, 2000 (the "Restated
                  Shareholders' Agreement")), each holder of Series A Preferred,
                  Series B Preferred and Series C Preferred (collectively, the
                  "Preferred Shareholders") have certain preemptive and
                  participation rights which entitle it to purchase and sell up
                  to its Preemptive Share (as such term is defined in the
                  Restated Shareholders' Agreement) of such New Securities.

                  Each Preferred Shareholder has certain conversion rights
                  pursuant to Article III, Part B, Section 3 of the Restated
                  Certificate which entitle it to convert each share of
                  Preferred Stock into such number of shares of Common Stock as
                  is determined by dividing $5.62 (with respect to a holder of
                  Series A Preferred), $12.07 (with respect to a holder of
                  Series B Preferred) or $18.23 (with respect to a holder of
                  Series C Preferred) by the Conversion Price (as such term is
                  defined in the Restated Certificate). The initial Conversion
                  Price is $5.62(with respect to a holder of Series A
                  Preferred), $12.07 (with respect to a holder of Series B
                  Preferred) or $18.23 (with respect to a holder of Series C
                  Preferred). However, if the Company should issue Additional
                  Shares of Common Stock (as such term is defined in the
                  Restated Certificate), the Conversion Price may, under certain
                  circumstance presented by the Restated Certificate be adjusted
                  to account for such additional issues.

                  Each Preferred Shareholder is entitled to certain dividend
                  rights under Article III, Part B, Section 6 of the Restated
                  Certificate which entitle it to receive cumulative, annual

<PAGE>   3

                  dividends at a rate equal to forty-five cents ($0.45) (with
                  respect to a holder of Series A Preferred), ninety-seven cents
                  ($0.97) (with respect to a holder of Series B Preferred) or
                  one dollar and forty six cents ($1.46) (with respect to a
                  holder of Series C Preferred) per annum per share. Dividends
                  payable on Preferred Stock may, at the Company's option, be
                  paid either in cash or in shares of Common Stock.

                  Pursuant to that certain Letter Agreement dated January 15,
                  1998 by and between the Company and Carl Zeiss Holding Co.
                  ("Zeiss"), Zeiss and Company have agreed that Zeiss shall have
                  the right to certain anti-dilution rights to which the holders
                  of the Series A Preferred are entitled under the conversion
                  rights provisions of the Restated Certificate.

                  On July 21, 1999, the Company entered into an agreement which
                  provided for an equipment financing line of credit with Oxford
                  Venture Finance, LLC ("OVF"). Under the agreement, OVF is
                  entitled to receive warrants to purchase shares of the
                  Company's common stock (with an exercise price of $6.60) equal
                  to 2.35% of the borrowings under the line of credit divided by
                  the $6.60 exercise price.

                  Except as set forth in this Section 3.3, there are no
                  outstanding options, warrants, rights (including conversion or
                  preemptive rights and rights of first refusal or similar
                  rights) for the purchase or acquisition from the Company of
                  any of its shares of capital stock.

                  c. AUTHORIZATION. The third sentence of Section 3.4 of the
         Purchase Agreement is hereby deleted in its entirety and replaced with
         the following:

                  The execution and delivery by the Company of this Agreement
                  and compliance herewith, and the offer, and subject to
                  obtaining requisite approvals of the Company's stockholders,
                  the issuance and sale of the Shares will not, with or without
                  notice or the passage of time or both, result in any violation
                  of and will not conflict with, or result in a breach of any of
                  the terms of, or constitute be affected, or result in the
                  creation of any mortgage, pledge, lien, encumbrance or charge
                  upon a default under any provision of, (i) any state or
                  federal law to which the Company is subject, (ii) the Amended
                  and Restated Certificate or By-Laws, or (iii) any material
                  mortgage, indenture, agreement, instrument, judgment, decree,
                  order, rule or regulation or other restriction to which the
                  Company is a party or by which it or any of its property is
                  bound, or may any of the properties or assets of the Company
                  pursuant to any such term or give any other person or entity
                  the right to accelerate the time for performance of any
                  obligation of the Company; provided, however, that,
                  notwithstanding the foregoing, the Purchaser, the holders of
                  Preferred Stock and Carl Zeiss Holding Co. have registration
                  rights that are similar in certain respects and may be
                  construed as competing rights.

                  d. NO MATERIAL ADVERSE CHANGE. The following provision shall
         be added as Section 3.12 of the Purchase Agreement:

                  Since June 9, 2000, the Company has not experienced any
                  occurrence or event which, to the knowledge of the Company, is
                  likely to result in a material adverse effect on the Company.

         4. RATIFICATION AND CAPITALIZED TERMS. Except as herein revised,
         Beckman and the Company hereby ratify and reaffirm the Purchase
         Agreement

<PAGE>   4

         in its entirety, and the Purchase Agreement remains in full force and
         effect. Capitalized terms used but not defined herein shall have the
         meanings ascribed to such terms in the Purchase Agreement.

         IN WITNESS WHEREOF, the parties hereto have caused this First Amendment
to Common Stock Purchase Agreement to be executed as of the day and year first
above written.

Attest:                             Beckman Coulter, Inc.

                                    By:         [Illegible]
----------------------------           --------------------------------
                                    Name:
                                    Title:

Attest:                             Cellomics, Inc.

                                    By: /s/ D. LANSING TAYLOR
-----------------------------          --------------------------------
                                         D. Lansing Taylor
                                         President<PAGE>   1
                                                                   Exhibit 10.22

                                 CELLOMICS, INC.
                              635 WILLIAM PITT WAY
                              PITTSBURGH, PA 15238

                                 October 2, 2000

Beckman Coulter, Inc.
Attn: Hung Bui
4300 North Harbor Boulevard
Mail Stop B34AA
Fullerton CA 92834-3100

         Re:      Cellomics, Inc. - Notice of Sale

         Dear Beckman Coulter, Inc.:

         Cellomics, Inc. (the "Company") has entered into a transaction through
which it issued and sold in a private placement One Million Six Hundred
Forty-Five Thousand Six Hundred Thirty-Nine (1,645,639) shares of the Company's
Series C Preferred Stock (the "Shares") at Eighteen and 23/100 Dollars ($18.23)
per share (the "Series C Financing") upon certain terms and conditions as are
set forth in that Series C Preferred Stock Purchase Agreement dated September
27, 2000 by and among the Company and the Purchasers listed on Exhibit A
thereto.

         Pursuant to Section 7.1(b) of that certain Common Stock Purchase
Agreement dated June 9, 2000 (the "Agreement") by and between the Company and
Beckman Coulter, Inc. ("Beckman"), Beckman is entitled to certain purchase
rights in the event that the Company sells certain Common Stock or Common Stock
Equivalents (as such terms are defined in the Agreement). Specifically, Beckman
is entitled to purchase that number of shares of Common Stock sufficient to
maintain Beckman's proportionate beneficial ownership interest in the Company
(the "Purchase Rights"). Pursuant to the Agreement, Beckman may exercise its
Purchase Rights by delivering a written notice of acceptance (the "Acceptance
Notice") to the Company within twenty (20) days after Beckman receives written
notice of the Company's sale of Common Stock or Common Stock Equivalents.

         The Shares sold in the Series C Financing constitute Common Stock
Equivalents within the meaning of the Agreement, thereby triggering the Purchase
Rights and entitling Beckman to purchase up to Fifty-Two Thousand Seven Hundred
Eleven (52,711) shares of Common Stock at Eighteen and 23/100 Dollars ($18.23)
per share.

         This letter constitutes the written notice of the sale (the "Notice of
Sale") as required by Section 7(b) of the Agreement in respect of the Series C
Financing. Attached to this Notice of Sale are: (1) Amendment to Common Stock
Purchase Agreement; (2) Acceptance Notice; (3) Waiver of 20-Day Exercise Period;
and (4) Wire Instructions.

         In the event that Beckman desires to purchase any portion of its
Purchase Rights, please have a duly authorized representative of Beckman execute
the attached Amendment to Common

<PAGE>   2

Stock Purchase Agreement, Acceptance Notice and Waiver of 20-Day Exercise
Period, and wire an amount equal to $18.23 multiplied by the number of shares
which Beckman desires to exercise its Purchase Rights to acquire (which would be
a maximum of Nine Hundred Sixty Thousand Nine Hundred Twenty-One and 53/100
Dollars ($960,921.53) in the event that Beckman desires to exercise Purchase
Rights for all 52,711 shares which it is entitled to acquire) on or before
October 11, 2000. However, regardless of whether Beckman chooses to purchase any
portion of its Purchase Rights for the Series C Financing, please execute and
return the attached Waiver of 20-Day Exercise Period.

         If you should have any questions, please call.

                                              CELLOMICS, INC.

                                              By: /s/ LEROY L. METZ
                                                  ----------------------
                                                  LeRoy L. Metz
                                                  Secretary

<PAGE>   3

             ACCEPTANCE NOTICE - SERIES C PREFERRED STOCK FINANCING

         Pursuant to Section 7(b) of that certain Common Stock Purchase
Agreement dated June 9, 2000 (the "Agreement") by and between Beckman Coulter,
Inc. ("Beckman") and Cellomics, Inc. (the "Company"), please allow this letter
to serve as the required Acceptance Notice that:

         In connection with the issuance and sale of 1,645,639 shares of Series
         C Preferred Stock of the Company at $18.23 per share and in accordance
         with the purchase rights provided to Beckman in the Agreement, Beckman
         hereby elects to purchase __________ shares of Common Stock of
         Cellomics, Inc. at $18.23 per share and hereby agrees to wire an amount
         equal to $_________________________.

                                            Beckman Coulter, Inc.

                                            By: __________________________
                                            Name: ________________________
                                            Title: _______________________

<PAGE>   4

                        WAIVER OF 20-DAY EXERCISE PERIOD
                       SERIES C PREFERRED STOCK FINANCING

         Pursuant to Section 7(b) of that certain Common Stock Purchase
Agreement dated June 9, 2000 (the "Agreement") by and between Beckman Coulter,
Inc. ("Beckman") and Cellomics, Inc. (the "Company"), Beckman is entitled to
certain purchase rights (the "Purchase Rights") in the event that the Company
sells certain Common Stock and Common Stock Equivalents (as such terms are
defined in the Agreement). The Company has entered into a transaction through
which it issued and sold in a private placement One Million Six Hundred
Forty-Five Thousand Six Hundred Thirty-Nine (1,645,639) shares of the Company's
Series C Preferred Stock at Eighteen and 23/100 Dollars ($18.23) per share (the
"Series C Financing") upon certain terms and conditions as are set forth in that
Series C Preferred Stock Purchase Agreement dated September 27, 2000 by and
among the Company and the Purchasers listed on Exhibit A thereto. Beckman may
exercise its Purchase Rights during the period commencing on the date that
Beckman receives the Company's notice of the sale (the "Notice of Sale") and
ending twenty (20) days thereafter. By the signature below, Beckman acknowledges
receipt of the Company's Notice of Sale and expressly waives the 20-day period
during which to exercise its Purchase Rights in the Company's Series C
Financing.

                                           Beckman Coulter, Inc.

                                           By: ____________________________
                                           Name: __________________________
                                           Title: _________________________

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00017-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00017-of-00352.parquet"}]]