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                                                                   EXHIBIT 10.10

        AGREEMENT FOR AN EXCLUSIVE ALLIANCE TO DEVELOP, MANUFACTURE AND
             MARKET A CHIP-BASED SCREENING SYSTEM FOR CELL ANALYSIS

This is an agreement executed this Twenty-sixth day of October, 1999,
hereinafter the "Effective Date") between Cellomics, Inc., 635 William Pitt
Way, Pittsburgh, PA. 15238 (hereinafter CELLOMICS) and ACLARA BioSciences Inc.
1288 Pear Avenue, Mountain View, CA 94043-1432 (hereinafter ACLARA).

                                    RECITALS

Whereas CELLOMICS has expertise in drug discovery, patterning cells on
substrates, cell analyses, luminescence detection, imaging science and
informatics;

Whereas ACLARA has expertise in microfluidics, design and engineering of
microdevices in plastic, and process engineering;

Whereas CELLOMICS and ACLARA desire to form a development, manufacturing and
marketing alliance to produce a Screening System for the life sciences to
perform Cell-based Assays.

Now, therefore, in consideration of the covenants and conditions contained
herein, the Parties, intending to be legally bound, agree as follows:

1.   Definitions

1.1  "Cassette" means an assembled unit comprising an operable combination of a
     Cell Plate and Microfluidic Plate.

1.2  "Cell-based Array" means any assay in which a biological target molecule or
     organelle is analyzed in, on and [*]. The cells can be from any life form
     including but not limited to bacteria, animals and plants.

1.3  "Cell Plate" means a glass or plastic plate material having a modified
     surface that supports selective adhesion of cells in discrete regions.

1.4  "EAP" shall mean an Early Access Partner. This is a third party that has
     executed a TAP Agreement approved by the JSC pursuant to which such third
     party (i) is provided access to Prototypes during the Development Phase and
     (ii) pays a fee for having early access under the applicable TAP.

1.5  "High Content Screening (HCS)" means the activity or status of cells in the
     Cassette [*].

1.6  "High Throughput Screening (HTS)" means the measurement of single values
     that represent the average or total of a signal obtained from a single
     well in a Cassette,

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     regardless of whether the signal is produced intra- or extracellularly. The
     single values will be obtained as a group of values as to different
     candidate compounds or different indications resulting from the same
     compound.

1.7  "Intellectual Property Milestone" shall be when the Parties complete a
     Prototype and the aggregate commitment from the TAP shall be [*] based on
     individual EAP fees of at least [*].

1.8  "JSC" shall mean the Joint Steering Committee, which will be composed of
     equal numbers of members from both CELLOMICS and ACLARA, not to exceed a
     total of eight, which members may be changed from time to time by the Party
     whom they represent, and to be chaired by the Project Leaders for the
     Parties.

1.9  "Liquid Transfer System" means any system used for transferring materials
     to the Cassette.

1.10 "Luminescence-based Reagents" are reagents that result in light emission
     for use in Cell-based Assays.

1.11 "Microfluidic Plate" means microfluidic device of an electrically
     non-conducting material designed to mate with the Cell Plate to [*].

1.12 "Microplate" means a standard multiwell plate most commonly of 96 or 384
     wells, but also available in 6, 12, 24, 48, 1536 and other formats with
     overall dimensions of about 3.5 x 4.5 cm.

1.13 "Program" shall mean a research program to develop a Screening System as
     set forth in the Workplan.

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1.14  "Prototype" shall mean a development stage Screening System meeting all or
      most of the specifications set forth in the applicable Workplan, however,
      not in a format useful for general sale and commercial distribution. A
      Prototype is typically suitable for delivery to an EAP.

1.15  "Reader" shall mean the optical system and accompanying software
      developed for reading the Luminescence signals from the cells.

1.16  "Revenue Source" is any source of revenues to support the Program other
      than internal sources, including but not limited to government grants, EAP
      fees, funds from the other Party and funds from collaborators other than
      a Party.

1.17  "Robotics" means the mechanical units for assembling and moving the
      components necessary for performing a Cell-based Assay with a Cassette.

1.18  "Screening System" shall mean the Cassette, Robotics, Reader, Liquid
      Transfer System, software and such other integrated peripheral devices to
      conduct High Throughput and/or High Content Screening, including
      disposables. The Screening System shall be all of the hardware and
      software to provide a complete system for performing Cell-based Assays
      (except for the Luminescence-based Reagents and such other reagents as
      may be used for Cell-based Assays).

1.19  "TAP" shall mean Technology Access Program between ACLARA and CELLOMICS
      with companies which shall serve as EAPs.

1.20  "Workplan" shall list goals and tasks detailing the actual work expected
      to be done, with timelines, budget and a delineation of responsibilities.

2.   Development

      2.1  The "Field" of this collaboration is the development of an automated
           system for [*]. It is an essential term of this agreement that
           CELLOMICS agrees to work exclusively with ACLARA on any and all
           matters involving microfluids in Cell-based Assays and ACLARA
           agrees to work exclusively with CELLOMICS on any and all matters
           involving Cell-based Assays during the Program.

      2.2  This Agreement will become effective on the Effective Date.

      2.3  CELLOMICS is attempting to obtain [*] to be permitted to utilize [*]
           to support ACLARA's research effort for the [*] of the Program.
           Whether or not CELLOMICS ever obtains such approval from [*],
           CELLOMICS is obligated to and hereby commits to pay [*] to support
           ACLARA's said research for the [*] of the

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           Program in [*]. During the period in which CELLOMICS is paying
           ACLARA, ACLARA shall provide CELLOMICS with a statement of the cost
           allocated to the Program as determined in accordance with reasonable
           accounting procedures used internally by ACLARA within thirty (30)
           days of receipt of the quarterly check due ACLARA. The dates on
           which such payments are due may be changed in accordance with the
           date of initiation of work by ACLARA and the rate at which employees
           are hired by ACLARA to perform the Program.

     2.4   During the first year of the term of this agreement ("First Year"),
           the Parties agree to work in accordance with the Workplan set forth
           in Appendix A, with the goal to have a Prototype of the Cassette by
           the first anniversary of the Effective Date. The goal during the
           First Year is to optimize the Cell Plate and Microfluidic Plate
           design and interfacing to enable fabrication of a functional
           Cassette. This Cassette is intended to have the specifications for
           and serve as a testbed for a [*]. In addition, it is intended that
           the Parties will use this Cassette as a working Prototype in a TAP
           program. Development of the Cassette Prototype will be directed to
           enable: [*]. During the First Year and thereafter, each Party will
           provide written reports with thirty (30) days of the end of each
           calendar quarter of the progress it has made during such quarter and
           the work to be performed in the next quarter and a written summation
           of the work accomplished at the end of each calendar year within
           thirty (30) days of the end of such calendar year.

     2.5.  Notwithstanding the intention to achieve the goals of the Workplan
           for the First Year, it is understood that in order to staff the
           Program, ACLARA and CELLOMICS will be required to hire new personnel
           or transfer existing personnel as they may become available. While
           each Party will act diligently to staff the Program in accordance
           with the Program's needs and available funding, the timing of such
           hires or transfers is not completely within the control of the
           Parties and the schedule of the Workplan may be delayed. At each
           quarterly meeting of the JSC, the accomplishment of the previous
           quarter, and the available funding, committed or to be committed,
           will be evaluated and the Workplan modified, if necessary, in light
           of the circumstances then pertaining.

           2.5.i.     If prior to the occurrence of the Intellectual Property
                   Milestone there appears to either Party to be an
                   insufficient Revenue Source at that time or in the
                   reasonably foreseeable future to support the Program in the
                   amounts required by each Party for its performance, the JSC
                   shall review the situation and report to the respective
                   CEO's its recommendation as to how to proceed within sixty
                   (60) days of notification by either Party that such Party
                   believes there is an insufficient Revenue Source to support
                   the Program. If the CEOs cannot agree within sixty (60) days
                   of receiving

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                  notification from the JSC as to how to proceed, either Party
                  may terminate this Agreement upon giving prompt notice of
                  termination to the other Party without obligation to license
                  the other party under the terminating Party's intellectual
                  property. If the Program is terminated for other than material
                  breach prior to the completion of the Intellectual Property
                  Milestone, the parties will negotiate in good faith to allow a
                  continuing party to continue the Program.

         2.5.ii.  Notwithstanding Paragraph 2.5.i, after the Intellectual
                  Property Milestone has been achieved, the terminating Party
                  will be obligated to license the continuing Party under the
                  terminating Party's intellectual property to continue to
                  develop and commercialize the Prototype and Screening System
                  as hereinafter provided. Upon termination by one Party for
                  other than material breach, with the Intellectual Property
                  Milestone having been achieved, the other Party may continue
                  the Program and the terminating Party agrees to enter into
                  negotiations within thirty (30) days of such termination with
                  the other Party over the terms of such license which the
                  terminating Party is obligated to license to the continuing
                  Party under its intellectual property, both background and
                  foreground, on reasonable terms and conditions to make, use
                  and sell Screening Systems substantially conforming to the
                  Screening System which was to be jointly developed.

       2.6   Assuming financing is obtained as required to support the Program
             for the second and third years of the term of this Agreement, or
             such other periods in which the goals of these years are to be
             fulfilled as determined by the JSC, a Screening System will be
             developed, which is intended to offer a complete solution to the
             need for flexibility in Cell-based Assays starting with an initial
             focus on [*]. The Screening System will be designed to have the
             ability to provide a complete portfolio of assays including [*].
             The Screening System will offer a ready-to-use and easy-to-use
             solution for the life scientist and further will promote
             penetration of sophisticated Cell-based Assays HCS in drug
             discovery. The target pharmaceutical customer for the Screening
             System is an entity with significant biological expertise in
             primary screening, a therapeutic group or a specialty such as [*].

       2.7   The development program for [*] of the term of this agreement is
             set forth in Appendix B with the intention of developing a
             Screening System. The 3D Cassette will have a high density plumbing
             architecture for selective addressing of a high density of
             micro-arrayed cells on the Cell Plate. The initial design and
             prototypes will focus on multiples of 96 well patterns in a
             footprint ranging from [*].

       2.8   CELLOMICS shall be responsible for identifying sources for the
             Robotics, Reader and such other equipment, which is not available
             from or to be developed

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            by the Parties to this agreement. Selection of one or more sources
            for providing the additional equipment will begin not later than
            four (4) months after a Cassette Prototype has been shown to be
            satisfactory to the Parties. CELLOMICS shall submit to ACLARA a
            list of potential sources of producing the components of the
            Screening System not already being produced by either ACLARA or
            CELLOMICS. ACLARA and CELLOMICS shall mutually agree on the
            priority in which these sources are to be approached, and
            additional candidates added, neither party shall unreasonably
            withhold such agreement. Such third party(s) and the terms upon
            which they agree to participate in developing the Screening System
            shall be proposed and negotiated by CELLOMICS and shall be subject
            to the review, but not the approval of the JSC.

      2.9   In [*] of the term of this Agreement, the Parties will direct their
            efforts to the development of a Screening System commercial product.
            The Prototype developed in [*] is to be taken through the final
            phase of the product development cycle and to establish
            manufacturing, marketing and sales.

      2.10  A complete Screening System will include all the components
            required by a user to take a library of compounds stored in a
            Microplate format and screen the library of compounds against a
            target, producing a data set in a standard database format for ease
            of access. The responsibilities of the Parties as to the following
            components that are required to accomplish this goal are:

         -  CELLOMICS
         [*]

         -  ACLARA
         [*]

3.    Funding

      3.1   A budget is set forth for the First Year in Appendix B. Promptly
            after execution of this Agreement, the Parties will submit a
            proposed budget for [*], which budget shall be subject to review,
            modification, and approval by the JSC. These budgets will be the
            basis for [*] and provide for the division of money received from
            [*] between the Parties.

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            3.2.  Not later than three (3) months after initiation of the
                  Workplan, the JSC will prepare and submit a budget to [*]
                  based on the budgets submitted by the Parties requesting an
                  increase in the total funding for both companies to accelerate
                  the development of the Screening System. Not later than [*],
                  the Parties will prepare and submit a [*] grant. The budget
                  may reflect provision for sources of components of the
                  Screening System, which the Parties do not intend to develop
                  or supply.

            3.3   CELLOMICS and ACLARA will jointly prepare a TAP to attract
                  companies as EAPs that will fund the Program. CELLOMICS and
                  ACLARA will jointly make presentations to the pharmaceutical
                  industry. The Parties will develop jointly the basic terms for
                  a TAP, which shall be the basis for entering into agreements
                  with EAPs. The TAP will be developed not later than one (1)
                  month from the completion of a satisfactory Cassette
                  Prototype.

      4.    Commercialization plan

            4.1.  Final product development and component manufacturing: The
                  Prototype completed in [*] and delivered as a beta test system
                  to at least [*] EAPs in [*] will be developed into a Screening
                  System component for manufacturing. ACLARA will be responsible
                  for final engineering and establishment of manufacturing
                  capability for the Microfluidic Plate. ACLARA is developing a
                  [*], and if applicable, ACLARA will contribute this to the
                  Screening System. If incremental development is required to
                  render this [*] applicable to the Screening System, the JSC
                  may adjust the Workplan accordingly. CELLOMICS will be
                  responsible for Cell Plates, all reagents, assays, and
                  protocols. CELLOMICS will work to ensure that the components
                  which neither Party intends to produce are made available from
                  a third party and are available for commercialization of the
                  Screening System. CELLOMICS will be responsible for the final
                  development and manufacturing of the remaining components of
                  the Screening System.

            4.2.  Manufacturing of the integrated system: The final
                  manufacturing, packaging and delivery of [*] and other
                  Cell-based Assay reagents, Cassettes and Screening Systems to
                  customers will be the responsibility of CELLOMICS. Prior to
                  the initiation of manufacturing of a Cassette, the Parties
                  will enter into a supply agreement in which ACLARA will be
                  responsible for delivering to CELLOMICS, or a third party
                  designated by CELLOMICS, sufficient quantities of Microfluidic
                  Plates for packaging with Cell Plates. Such supply agreement
                  will provide for indemnification of the other Party on
                  conventional terms for the intentional, willful, or negligent
                  act or failure to act of one Party, giving rise to a claim
                  against the other Party. The supply terms for ACLARA's
                  delivery to CELLOMICS shall be conventional, giving due regard
                  to

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          the size of the batches required, the effect of volume on price,
          agreements with third parties for manufacture of the Microfluidic
          Plates and the time required for initiating a run of Microfluidic
          Plates. CELLOMICS will provide ACLARA with sales projections on a
          rolling basis. Inventory shall be the responsibility of CELLOMICS.

     4.3. Deliver Production Systems: For all life science applications,
          CELLOMICS will have full responsibility for ensuring that all
          components of the Screening System are available for marketing,
          marketing of the Screening System, and providing support for the
          Screening Systems and its components. The target markets for these
          systems will include, but not be limited to pharmaceutical discovery
          and development, clinical diagnostics, agriculture biotech, and basic
          biomedical research.

     4.4. Product Designation: ACLARA's name and trademark shall appear
          prominently on the Microfluidic Plate and CELLOMICS shall give due
          credit for ACLARA's contributions in its labeling, advertising and
          promotion. Statements made by CELLOMICS concerning ACLARA shall be
          subject to review and approval by ACLARA, which approval shall not be
          unreasonably withheld.

     4.5. Reader Designation: CELLOMICS's name and trademark shall be use din a
          primary capacity and ACLARA's name and trademark shall be use din a
          secondary capacity on the Reader and CELLOMICS shall give due credit
          for ACLARA's contributions in its labeling, advertising and promotion.
          Statements made by CELLOMICS concerning ACLARA shall be subject to
          review and approval by ACLARA, which approval shall not be
          unreasonably withheld.

5.   Revenue Sharing

     5.1  During the development and commercialization phase, the money obtained
          from third parties from a Revenue Source shall be divided to ensure
          that each Party's expenditure of its own money on a JSC approved
          Workplan is minimized. The exact division of [*] will be decided at
          the time of [*]. The division of TAP fees will be defined by the JCS,
          and approved by the CEO of both Parties, and written into a separate
          agreement between CELLOMICS and ACLARA before a TAP agreement is
          consummated. Funding from a collaborator other than the other Party
          will primarily be used for the purposes of the collaboration.

     5.2  Not later than the end of [*] the Parties shall initiate negotiations
          as to the division of income resulting from the sales of Screening
          Systems and its components. The division of the income will first be
          considered by the JSC with final approval of the CEO's from CELLOMICS
          and ACLARA. ACLARA shall receive from CELLOMICS [*] and a reasonable
          profit margin for items manufactured or supplied by ACLARA;
          Considerations in determining the division of remaining

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          income shall be the financial contribution of each of the Parties,
          except to the extent the Parties have been reimbursed any portion of
          their contribution by a Revenue Source, the novelty of their
          contributions, the value of the intellectual property that protects
          components of the Screening Systems, the competitive advantages
          provided by the contributions of the two Parties, the responsibilities
          of the two Parties in manufacturing, marketing and supporting the
          ongoing expenditures, the risks involved with the continuing
          investments, and the like. The income to ACLARA shall not be less than
          a reasonable royalty on patents and know-how contributed by ACLARA
          with the base being Screening Systems and components, where the
          royalty may vary as to whole Screening Systems and as to individual
          disposable Screening System components. Royalty shall not be paid
          twice for the same component of the Screening System. If there is no
          agreement between the Parties, the matter shall be given to mediation
          as provided for hereinafter. The exact mechanism for delivering the
          value to the Parties will be defined as the program proceeds toward
          commercialization. It may involve strict revenue sharing, licensing,
          royalties or some combination that will be defined by the JSC.

6.   Public Relations

     6.1  All press releases created by an originating Party shall be submitted
          to the other Party for approval and shall not be released without the
          prior written approval of the other Party. In the event of a dispute,
          the matter shall be submitted to the CEOs of the Parties and if the
          issue cannot be reconciled, there shall be no press release containing
          disputed subject matter.

     6.2  Prior to commercial introduction of a Screening System, all public
          presentation relating to this Program, not already made public,
          including Web postings, corporate presentations, investor relations,
          and marketing collateral, must be approved by the other Party, such
          approval not to be unreasonably withheld.

7.   Intellectual Property

     7.1  Ownership. Each of the Parties will own all intellectual property and
          inventions made by individuals who have a duty to assign to that Party
          and will jointly own all inventions co-invented by at least one
          inventor having a duty to assign to each Party. The Party owning the
          invention shall have the exclusive right to file worldwide for patent
          applications covering the invention.

     7.2  Joint Intellectual Property. CELLOMICS and ACLARA will jointly
          determine the advisability of filing a patent application. The JSC
          will appoint one of the Parties to be responsible to prepare, file,
          prosecute diligently and maintain such application(s). The Parties
          will share equally all reasonable costs incurred in

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          connection with such activities (i.e., the non-prosecuting Party will
          promptly reimburse the prosecuting Party), provided, however, that
          either Party may avoid its responsibility for such costs by assigning
          its rights in such Joint Intellectual Property to the other Party. In
          such an event, the other Party may decide at its sole discretion
          whether or not to file or continue prosecution of such applications.
          Also, the assigning Party will provide reasonable assistance to the
          assignee to facilitate the filing and prosecution of all such
          applications. Joint Intellectual Property will be jointly owned, and
          either Party is free to use such Joint Intellectual Property as it
          sees fit, outside the Field of this Agreement. CELLOMICS shall have
          the exclusive right to use such Joint Intellectual Property within the
          Field of this Agreement for the lessor of i) a period of five (5)
          years from the first commercial release of the Screening System, or
          ii) eight years (8) from the Effective Date. Thereafter, either Party
          may use such Joint Intellectual Property without accounting to the
          other Party.

     7.3  Rights. All inventions owned by ACLARA developed as part of the
          program having application to the Cell Plate shall be licensed to
          CELLOMICS on reasonable terms and conditions, if at the time of filing
          of a patent application for such invention, CELLOMICS agrees to pay
          [*] of the out-of-pocket costs of the filing, prosecution and
          maintenance of such application, continuing applications, foreign
          analogs, and Letters Patent issuing thereon. All inventions owned by
          CELLOMICS developed as part of the collaboration having application to
          the Microfluidic Plate shall be licensed to ACLARA on reasonable terms
          and conditions, if at the time of filing of a patent application for
          such invention, ACLARA agrees to pay [*] of the out-of-pocket costs of
          the filing, prosecution and maintenance of such application,
          continuing applications, foreign analogs, and Letters Patent issuing
          thereon.

     7.4  Licensing of Foreground technology. Technical know-how and patent
          rights developed as part of the Program shall be available on
          reasonable terms and conditions after termination of this Agreement in
          the event that one Party wishes to continue the Program.

     7.5  Licenses of Background Technology. Technical know-how and patent
          rights developed prior to initiation of the Program or outside of the
          Program may be licensed for a Screening System developed in the
          Program as set forth in Section 2.5.

     7.6  Label License. All products supplied by ACLARA to CELLOMICS will
          include a label license, granting CELLOMICS a license under ACLARA's
          intellectual property to use, offer to sell, and sell any such
          products for use in the Field, such label license being transferable
          to the purchasers of such products.

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     7.7. Confidentiality. All technical and business information given the
          recipient Party by the disclosing Party shall be assumed to be in
          confidence and if disclosed orally, shall be reduced to writing and
          delivered to the recipient within thirty (30) days of disclosure.
          Information received in confidence shall be used solely for the
          purposes of this Agreement and shall be disclosed to others who assume
          like duties of confidentiality. The restrictions on use and disclosure
          shall not apply where the information is or becomes generally known
          without failure on the part of the recipient; was known to the
          recipient prior to receipt from the discloser; or is given to the
          recipient by a third party who has the right to disclose the
          information, without restriction on use or disclosure. The obligations
          on use and disclosure shall terminate five (5) years from the
          termination of the Program.

8.   Surviving Rights/Termination

     8.1  Surviving Rights and Duties. The right to obtain licenses to
          intellectual property rights covering technology employed in the
          Program as provided for in this Agreement shall survive termination of
          this Agreement. Either Party shall have the right to a license from
          the other Party if such license is requested within two (2) years
          after termination of this Agreement.

     8.2  Termination. This Agreement may be terminated by either Party in the
          event of material breach by the other Party, upon giving sixty (60)
          days prior written notice of the intent to terminate, which
          termination will be effective if the breaching Party has not taken
          reasonable steps to correct the material breach. The right to
          terminate is in addition to all other rights the non-breaching Party
          may have against the breaching Party.

     8.3  Permissive termination. Either Party may terminate this Agreement,
          with the acceptance of the other.

9.   Governance

     9.1  Joint Steering Committee. The Program will be governed by the JSC. The
          JSC shall consist of at least one senior executive, one business
          director, and one technical director from each Party. The JSC will
          meet at least once per quarter, alternating between locations selected
          by ACLARA and CELLOMICS, to oversee activities under a Workplan. In
          particular, the JSC will monitor and support collaboration and/or
          supply relationships existing between ACLARA and CELLOMICS, review,
          recommend modifications to, and oversee the implementation of active
          Workplans, define deliverables for TAPs, approve EAPs, review the
          commercial feasibility of Screening Systems being developed under a
          Workplan, review the progress of the Workplan and funding, offer
          modifications to the Workplan in light of changed circumstances,
          discuss new commercial opportunities and develop the objectives and
          terms for additional Programs between the Parties that may be pursued.
          The JSC shall have the authority to make reasonable alterations or
          amendments to the Workplan, which

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               will be considered final after reduction to writing and
               attachment to the Agreement. Significant alterations to the
               Workplan must be approved by the CEO of both Parties. The JSC
               shall have the authority to recommend alterations or amendments
               to this Agreement, which shall not become final until reduced to
               writing and signed by the CEO of each of the Parties. Except as
               otherwise expressly provided herein, decisions of the JSC will be
               made by consensus.

          9.2  Dispute resolution. Should disputes arise, the Parties agree to
               negotiate in good faith to resolve the disputes. Disputes that
               cannot be resolved by the JSC within a reasonable period shall be
               submitted to the CEOs of the Parties. If agreement is still not
               reached, the Parties agree to submit disputes to mediation in
               accordance with the section 9.3, "Mediation", prior to seeking
               any other remedy.

          9.3  Mediation. If the Parties are unable to resolve by negotiation
               within forty-five days of the disputing Party's written request
               for dispute resolution (or such other time period expressly set
               forth in this Agreement), or if the Parties fail to meet within
               twenty (20) days after such notice, the Parties shall endeavor to
               settle the dispute by mediation administered by the American
               Arbitration Association ("AAA") pursuant to the Commercial
               Mediation Rules of the AAA the time of submission prior to
               resorting to any other remedy. Mediation shall be held in a
               location to be decided later. The mediator appointed to assist
               the Parties must possess such credentials as qualify said
               mediator as (1) either an expert in the field being mediated or
               (2) at a minimum as reasonably familiar with the industries and
               specific applications as will enable the mediator to quickly
               understand and assist the Parties in dealing with the issues that
               are in dispute. Notwithstanding the foregoing, to the extent that
               any controversy or claim hereunder gives rise to a prayer for
               injunctive relief, equitable action or specific performance, the
               aggrieved Party shall have the right to commence such an action
               in any court of competent jurisdiction.

10.  Representations and Warranties

10.1 Authority. Each Party hereby represents and warrants to the other that it
     has full power and authority to enter into this agreement and to consummate
     the transactions contemplated hereby. This agreement has been duly executed
     and delivered and constitutes a valid and binding obligation of the Party,
     enforceable against it in accordance with its terms, except as such
     enforceability may be limited by bankruptcy, insolvency, reorganization,
     fraudulent conveyance, moratorium or similar laws affecting creditors'
     rights generally from time to time in effect or by general equitable
     principles.

10.2 Corporate Organization and Authority. Each Party hereby represents and
     warrants to the other that it is a corporation duly organized, validly
     existing and in good standing under the laws of Delaware as to CELLOMICS
     and California as to ACLARA and has all corporate power and authority to
     carry on its business as

CONFIDENTIAL

                                      -12-
<PAGE>   13
        now being conducted and to own its properties, is duly qualified and in
        good standing to do business in every jurisdiction in which such
        qualification is necessary because of the nature of the property owned,
        leased or operated by it or the nature of the business conducted by it
        except where the failure to be so qualified would not have a material
        adverse effect.

10.3    Ability to Carry Out the Agreement: Consents and Waivers. Each Party
        hereby represents and warrants to the other that the execution and
        delivery of this agreement does not, and the consummation of the
        transactions contemplated hereby will not, conflict with, or result in
        any violation of or default (with or without notice or lapse of time, or
        both) under, or give rise to a right of termination under, or accelerate
        the performance required by, or result in the creation of any lien,
        security interest, charge, increase in liability or other encumbrance
        upon any of its assets under, any provision of:

                (i)   any law, statute, rule, regulation or judicial or
                      administrative decision;

                (ii)  any certificate of incorporation or by-laws;

                (iii) any mortgage, deed of trust, lease, note, shareholders'
                      agreement, bond, indenture, contract or other instrument
                      or agreement; or

                (iv)  any judgment, order, writ, injunction or decree of any
                      court, governmental body, administrative agency or
                      arbitrator relating to it;

                (v)   other than conflicts, violations, defaults, right of
                      termination or encumbrances which could not reasonably be
                      expected to have a material adverse effect on the
                      enforceability or validity or the agreement.

10.4    Litigation. Each Party hereby represents and warrants to the other that
        there is no action, suit, or governmental, administrative or regulatory
        proceeding or investigation pending or, to the knowledge of the Party,
        threatened against it at law, in equity or otherwise, in, before, or by
        any court or governmental agency or authority which could reasonably be
        expected to have a material adverse effect on this agreement or the
        transactions contemplated therein. ACLARA is presently involved solely
        in two pieces of litigation; being sued for misappropriation of trade
        secrets; and suing for patent infringement.

10.5    Year 2000. Each Party hereby represents and warrants to the other that
        software, hardware, equipment and systems owned, leased or licensed by
        it and used in the conduct of its business are Year 2000 Compliant.

CONFIDENTIAL

                                      -13-
<PAGE>   14
10.6    Regulatory Filings. Each of the Parties hereto will furnish to the other
        Party hereto such necessary information and reasonable assistance as
        such other Party may reasonably request in connection with its
        preparation of necessary filings or submissions to any governmental
        entity.

10.7    Announcement. Neither Party nor their respective affiliates will issue
        any press release or other public announcement with respect to this
        agreement or the transactions contemplated hereby without the prior
        written approval of the other Party hereto (such approval not to be
        unreasonably withheld, conditioned or delayed).

10.8    Indemnification. Each Party agrees to defend, indemnify and hold
        harmless the other and its respective successors and assigns against
        and in respect of:

        (a) any and all losses, damages, deficiencies or liabilities ("Damages")
            caused by, resulting or arising from or otherwise relating to any
            material failure by a Party to perform or otherwise fulfill or
            comply with any undertaking or other agreement or obligation to be
            performed, fulfilled or complied with by the Party resulting from
            its gross negligence, willful misconduct or arising from or
            otherwise relating to any material breach of any representation or
            warranty of the Party contained in this agreement.

10.9    Entire Agreement. The Agreement (including the appendices attached
        hereto, all of which are part hereof) contain the entire understanding
        of the Parties hereto with respect to the subject matter contained
        herein, and supersede and cancel all prior agreements, negotiations,
        correspondence, undertakings and communications of the Parties, oral or
        written, respecting such subject matter. There are no restrictions,
        promises, representations, warranties, agreements or undertakings of any
        Party hereto with respect to the transactions under this Agreement
        other than those set forth herein or therein or made hereunder or
        thereunder.

10.10   Amendments. This agreement may be amended only by a written instrument
        executed by the Parties or their respective successors or assigns.

10.11   Headings; References. The article and section headings contained in
        this agreement are for reference purposes only and shall not affect in
        any way the meaning or interpretation of this agreement. All references
        herein to "Articles," "Sections," "Schedules," or "Appendices" shall be
        deemed to be references to Articles or Sections hereof or Schedules or
        Appendices hereto unless otherwise indicated.

11.     Notices

        11.1.  Notices may be given to an officer of a Party by;

CONFIDENTIAL

                                      -14-
<PAGE>   15
personal delivery, fax or registered mail addressed as follows:
overnight delivery by an internationally recognized courier service

If to ACLARA Biosciences Inc.:
Joseph M. Limber
President and CEO
ACLARA Biosciences, Inc.
1288 Pear Avenue
Mountain View, CA 94043-1432
FAX (650) 210-1210

If to CELLOMICS, Inc.:
D. Lansing Taylor
President and CEO
CELLOMICS, Inc.
635 William Pitt Way
Pittsburgh, PA 15238
FAX (412) 826-3896

12.  Binding Effect

12.1 This agreement shall inure to the benefit of and be binding on each Party's
     successors in interest and assigns.

13.  Assignment

13.1 Either Party may assign this agreement only in connection with the sale or
     disposition of the entire business of such Party or that portion to which
     this agreement pertains. Either Party may assign this Agreement to an
     Affiliate(s) without permission of the other Party. Affiliate shall mean
     an entity controlling, controlled by, or under common control with a Party
     to this Agreement.

14.  Governing Law

14.1 This Agreement shall be interpreted in accordance with the local laws of
     the Party defending any action brought under this Agreement.

[Signature page Follows]

CONFIDENTIAL

                                      -15-
<PAGE>   16
 Signature Page for Agreement For An Exclusive Alliance To Develop, Manufacture
           And Market A Chip-Based Screening System For Cell Analysis

In Witness Whereof, this Agreement has been executed in multiple counterparts,
each of which shall constitute an original Agreement, on behalf of the Parties
by their authorized officers as of the date first written above:

CELLOMICS, INC.

Signature /s/ D. LANSING TAYLOR
          ------------------------------

Print D. Lansing Taylor
      ----------------------------------

Title President & CEO
      ----------------------------------

Date 10/26/99
     -----------------------------------

ACLARA BIOSCIENCES INC.

Signature /s/ JOSEPH M. LIMBER
          ------------------------------

Print Joseph M. Limber
      ----------------------------------

Title President & CEO
      ----------------------------------

Date October 26, 1999
     -----------------------------------

CONFIDENTIAL

                                      -16-
<PAGE>   17
                                   APPENDIX A

WORKPLAN
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -17-
<PAGE>   18
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -18-

<PAGE>   19
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -19-

<PAGE>   20
                                   APPENDIX B

                                  FUNDING PLAN

[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -20-
<PAGE>   21
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -21-
<PAGE>   22
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                    -22-
<PAGE>   23
[*]

CONFIDENTIAL

[*]  CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
     BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS
     AMENDED.

                                      -23-<PAGE>   1
                                                                   Exhibit 10.16

                            ACLARA BIOSCIENCES, INC.

                          EMPLOYEE STOCK PURCHASE PLAN

<PAGE>   2
                            ACLARA BIOSCIENCES, INC.

                          EMPLOYEE STOCK PURCHASE PLAN

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                     PAGE
<S>      <C>                                                                          <C>
1.       Definitions...................................................................1
2.       Stock Subject to the Plan.....................................................3
3.       Grant of Options..............................................................3
4.       Exercise of Options; Option Price.............................................5
5.       Withdrawal from the Plan......................................................6
6.       Termination of Employment.....................................................7
7.       Restriction upon Assignment...................................................7
8.       No Rights of Stockholders until Shares Issued.................................8
9.       Changes in the Stock and Corporate Events; Adjustment of Options..............8
10.      Use of Funds; No Interest Paid................................................9
11.      Dividends....................................................................10
12.      Amendment, Suspension or Termination of the Plan.............................10
13.      Administration by Committee; Rules and Regulations...........................10
14.      Designation of Subsidiary Corporations.......................................11
15.      No Rights as an Employee.....................................................11
16.      Term; Approval by Stockholders...............................................11
17.      Effect upon Other Plans......................................................12
18.      Conditions to Issuance of Stock Certificates.................................12
19.      Notification of Disposition..................................................13
20.      Notices......................................................................13
21.      Headings.....................................................................14
</TABLE>

                                       i
<PAGE>   3

                           ACLARA BIOSCIENCES, INC.

                          EMPLOYEE STOCK PURCHASE PLAN

     ACLARA BioSciences, Inc., a Delaware corporation (the "Company"), hereby
adopts the ACLARA BioSciences, Inc. Employee Stock Purchase Plan (the "Plan"),
effective as of _____________, 2000.

     The purposes of the Plan are as follows:

          (1)  To assist eligible employees of the Company and its Designated
     Subsidiary Corporations (as defined below) in acquiring stock ownership in
     the Company pursuant to a plan which is intended to qualify as an "employee
     stock purchase plan", within the meaning of Section 423(b) of the Code (as
     defined below).

          (2)  To help such employees provide for their future security and to
     encourage them to remain in the employment of the Company and its
     Subsidiary Corporations.

     1.   DEFINITIONS. Whenever any of the following terms is used in the Plan
with the first letter or letters capitalized, it shall have the following
meaning unless context clearly indicates to the contrary (such definitions to be
equally applicable to both the singular and the plural forms of the terms
defined):

          (a)  "Account" shall mean the account established for an Eligible
Employee under the Plan with respect to an Offering Period.

          (b)  "Agent" shall mean the brokerage firm, bank or other financial
institution, entity or person(s) engaged, retained, appointed or authorized to
act as the agent of the Company or an Employee with regard to the Plan.

          (c)  "Authorization" shall mean an Eligible Employee's payroll
deduction authorization with respect to an Offering Period provided by such
Eligible Employee in accordance with Section 3(b).

          (d)  "Base Compensation" of an Eligible Employee shall mean the gross
base compensation received by such Eligible Employee on each Payday as
compensation for services to the Company or any Designated Subsidiary
Corporation, excluding overtime payments, sales commissions, incentive
compensation, bonuses, expense reimbursements, fringe benefits and other
special-payments.

          (e)  "Board" means the Board of Directors of the Company.

          (f)  "Code" means the Internal Revenue Code of 1986, as amended.

          (g)  "Committee" means the committee of the Board appointed to
administer the Plan pursuant to Section 13.

                                       1

<PAGE>   4

          (h)  "Company" means ACLARA BioSciences, Inc., a Delaware corporation.

          (i)  "Date of Exercise" of any Option means the date on which such
Option is exercised, which shall be the last day of the Offering Period with
respect to which the Option was granted, in accordance with Section 4(a) (except
as provided in Section 9).

          (j)  "Date of Grant" of any Option means the date on which such Option
is granted, which shall be the first day of the Offering Period with respect to
which the Option was granted, in accordance with Section 3(a).

          (k)  "Designated Subsidiary Corporation" means any Subsidiary
Corporation designated by the Board in accordance with Section 14.

          (l)  "Effective Date" means the first day of the first Offering
Period, which shall be the date immediately preceding the first date on which a
share of Stock is traded on an exchange or quoted on Nasdaq or a successor
quotation system.

          (m)  "Eligible Employee" means an Employee of the Company or any
Designated Subsidiary Corporation: (i) who does not, immediately after the
Option is granted, own (directly or through attribution) stock possessing five
percent (5%) or more of the total combined voting power or value of all classes
of Stock or other stock of the Company, a Parent Corporation or a Subsidiary
Corporation (as determined under Section 423(b)(3) of the Code); (ii) whose
customary employment is for more than twenty (20) hours per week and (iii) whose
customary employment is for more than five (5) months in any calendar year. For
purposes of paragraph (i) above, the rules of Section 424(d) of the Code with
regard to the attribution of stock ownership shall apply in determining the
stock ownership of an individual, and stock which an Employee may purchase under
outstanding options shall be treated as stock owned by the Employee. During a
leave of absence meeting the requirements of Treasury Regulation Section
1.421-7(h)(2), an individual shall be treated as an Employee of the Company or
Subsidiary Corporation employing such individual immediately prior to such
leave.

          (n)  "Employee" shall mean an individual who renders services to the
Company or a Subsidiary Corporation in the status of an "employee", within the
meaning of Code Section 3401(c). "Employee" shall not include any director of
the Company or a Subsidiary Corporation who does not render services to the
Company or a Subsidiary Corporation in the status of an "employee", within the
meaning of Code Section 3401(c).

          (o)  "Offering Period" shall mean each six-month period commencing on
any November 1 and May 1 on or after the Effective Date; provided, however, that
the first Offering Period under the Plan shall be the period commencing on the
Effective Date and ending October 31, 2000. Options shall be granted on the Date
of Grant and exercised on the Date of Exercise, as provided in Sections 3(a) and
4(a), respectively.

          (p)  "Option" means an option to purchase shares of Stock granted
under the Plan to an Eligible Employee in accordance with Section 3(a).

                                       2

<PAGE>   5

          (q)  "Option Price" means the option price per share of Stock
determined in accordance with Section 4(b).

          (r)  "Parent Corporation" means any corporation, other than the
Company, in an unbroken chain of corporations ending with the Company if, at the
time of the granting of the Option, each of the corporations other than the
Company owns stock possessing 50% or more of the total combined voting power of
all classes of stock in one of the other corporations in such chain.

          (s)  "Payday" means the regular and recurring established day for
payment of Base Compensation to an Employee of the Company or any Subsidiary
Corporation.

          (t)  "Plan" means the ACLARA BioSciences, Inc. Employee Stock Purchase
Plan.

          (u)  "Stock" means the shares of the Company's Common Stock, $.001 par
value.

          (v)  "Subsidiary Corporation" means any corporation, other than the
Company, in an unbroken chain of corporations beginning with the Company if, at
the time of the granting of the Option, each of the corporations other than the
last corporation in an unbroken chain owns stock possessing 50% or more of the
total combined voting power of all classes of stock in one of the other
corporations in such chain.

     2.   STOCK SUBJECT TO THE PLAN. Subject to the provisions of Section 9
hereof (relating to adjustments upon changes in the Stock) and Section 12 hereof
(relating to amendments of the Plan), the Stock that may be sold pursuant to
Options granted under the Plan shall not exceed in the aggregate three hundred
thousand (300,000) shares of Stock. The shares of Stock sold pursuant to Options
granted under the Plan may be unissued shares or treasury shares of Stock, or
shares of Stock bought on the New York Stock Exchange or other
nationally-recognized exchange, or other market, for purposes of the Plan.

     3.   GRANT OF OPTIONS.

          (a)  Option Grants. The Company shall grant Options under the Plan to
all Eligible Employees in successive Offering Periods until the earlier of: (i)
the date on which the number of shares of Stock available under the Plan have
been sold, or (ii) the date on which the Plan is suspended or terminates. Each
Employee who is an Eligible Employee on the first day of an Offering Period
shall be granted an Option with respect to such Offering Period. The Date of
Grant of such an Option shall be the first day of the Offering Period with
respect to which such Option was granted. Each Option shall expire on the Date
of Exercise immediately after the automatic exercise of the Option in accordance
with Section 4(a), unless such Option terminates earlier in accordance with
Section 5, 6 or 9. The number of shares of Stock subject to an Eligible
Employee's Option shall equal the cumulative payroll deductions authorized by
such Eligible Employee in accordance with subsection (b) for the Option Period
(if any), divided by the Option

                                       3

<PAGE>   6

Price; provided, however, that the number of shares of Stock subject to such
Option shall not exceed five thousand (5,000) shares; and, provided, further,
that the number of shares of Stock subject to such Option shall not exceed the
number determined in accordance with subsection (c). The Company shall not grant
an Option with respect to an Offering Period to any individual who is not an
Eligible Employee on the first day of such Offering Period.

          (b)  Election to Participate; Payroll Deduction Authorization. Except
as provided in subsection (d), an Eligible Employee shall participate in the
Plan only by means of payroll deduction. Each Eligible Employee who elects to
participate in the Plan with respect to an Offering Period shall deliver to the
Company, not later than ten (10) days before the first day of the Offering
Period (or such shorter period as determined by the Committee in its
discretion), a completed and executed written payroll deduction authorization in
a form prepared by the Committee (the "Authorization"). An Eligible Employee's
Authorization shall give notice of such Eligible Employee's election to
participate in the Plan for the next following Offering Period (and subsequent
Offering Periods) and shall designate a whole percentage of such Eligible
Employee's Base Compensation to be withheld by the Company or the Designated
Subsidiary Corporation employing such Eligible Employee on each Payday during
the Offering Period. An Eligible Employee may designate any whole percentage of
Base Compensation which is not be less than one percent (1%) and not more than
fifteen percent (15%). An Eligible Employee's Base Compensation payable during
an Offering Period shall be reduced each Payday through payroll deduction in an
amount equal to the percentage specified in the Authorization, and such amount
shall be credited to such Eligible Employee's Account under the Plan.
Notwithstanding the preceding sentence, at the Committee's discretion payroll
deductions with respect to the initial Offering Period under the Plan may
commence as of the second Payday following the Effective Date and not the
initial Payday following the Effective Date. An Eligible Employee may change the
percentage of Base Compensation designated in the Authorization, subject to the
limits of this subsection (b), or may suspend the Authorization, at any time
during the Offering Period, provided, that any such change or suspension shall
become effective not later than ten (10) days after receipt by the Company. Any
Authorization shall remain in effect for each subsequent Offering Period, unless
the Eligible Employee submits a new Authorization pursuant to this subsection
(b), withdraws from the Plan pursuant to Section 5, ceases to be an Eligible
Employee as defined in Section 1(m) or terminates employment as provided in
Section 6.

          (c)  $25,000 Limitation. No Eligible Employee shall be granted an
Option under the Plan which permits his rights to purchase shares of Stock under
the Plan, together with other options to purchase shares of Stock or other stock
under all other employee stock purchase plans of the Company, any Parent
Corporation or any Subsidiary Corporation subject to the Section 423, to accrue
at a rate which exceeds $25,000 of fair market value of such shares of Stock or
other stock (determined at the time the Option or other option is granted) for
each calendar year in which the Option is outstanding at any time. For purpose
of the limitation imposed by this subsection, (i) the right to purchase shares
of Stock or other stock under an Option or other option accrues when the Option
or other option (or any portion thereof) first becomes exercisable during the
calendar year, (ii) the right to purchase shares of Stock or other stock under
an Option or other option accrues at the rate provided in the Option or other
option,

                                       4

<PAGE>   7

but in no case may such rate exceed $25,000 of the fair market value of such
Stock or other stock (determined at the time such Option or other option is
granted) for any one calendar year, and (iii) a right to purchase Stock or other
stock which has accrued under an Option or other option may not be carried over
to any Option or other option. This limitation shall be applied in accordance
with Section 423(b)(8) of the Code and the Treasury Regulations thereunder.

          (d)  Leaves of Absence. During a leave of absence meeting the
requirements of Treasury Regulation Section 1.421-7(h)(2), an Employee may
continue to participate in the Plan by making cash payments to the Company on
each Payday equal to the amount of the Employee's payroll deduction under the
Plan for the Payday immediately preceding the first day of such Employee's leave
of absence.

     4.   EXERCISE OF OPTIONS; OPTION PRICE.

          (a)  Option Exercise. Each Employee automatically and without any act
on such Employee's part shall be deemed to have exercised such Employee's Option
on the Date of Exercise to the extent that the balance then in the Employee's
Account is sufficient to purchase, at the Option Price, shares of the Stock
subject to the Option (including fractional shares).

          (b)  Option Price Defined. The option price per share of Stock (the
"Option Price") to be paid by an Employee upon the exercise of the Employee's
Option shall be equal to 85% of the lesser of: (i) the Fair Market Value of a
share of Stock on the Date of Exercise and (ii) the Fair Market Value of a share
of Stock on the Date of Grant. The Fair Market Value of a share of Stock as of a
given date shall be: (A) the closing price of a share of Stock on the principal
exchange on which the Stock is then trading, if any, on such date (or, if shares
of Stock were not traded on such date, then on the next preceding trading day
during which a sale occurred); (B) if the Stock is not traded on an exchange,
but is quoted on Nasdaq or a successor quotation system, (I) the last sales
price (if the Stock is then listed as a National Market Issue under the NASD
National Market System), or (II) the mean between the closing representative bid
and asked prices (in all other cases) for a share of Stock on such date (or, if
shares of Stock were not traded on such date, then on the next preceding trading
day during which a sale occurred) as reported by Nasdaq or such successor
quotation system; (iii) if the Stock is not publicly traded on an exchange and
not quoted on Nasdaq or a successor quotation system, the mean between the
closing bid and asked prices for a share of Stock on such date (or, if shares of
Stock were not traded on such date, then on the next preceding trading day
during which a sale occurred), as determined in good faith by the Committee; or
(iv) if the Stock is not publicly traded, the fair market value of a share of
Stock established by the Committee acting in good faith.

          (c)  Book Entry/Share Certificates. As soon as practicable after the
purchase of shares of Stock upon the exercise of an Option by an Employee, the
Company shall issue the shares of Stock to such Employee and such shares shall
be held in the custody of the Agent for the benefit of the Employee. The Company
or the Agent shall make an entry on its books and records indicating that the
shares of Stock purchased in connection with such exercise (including any
partial share) have been duly issued as of that date to such Employee. An
Employee shall

                                       5

<PAGE>   8

have the right at any time to request in writing a certificate or certificates
for all or a portion of the whole shares of Stock purchased hereunder. Upon
receipt of an Employee's written request for any such certificate, the Company
shall (or shall cause the Agent to), within ten (10) days after the date of such
receipt, deliver any such certificate to the Employee; provided, however, that
no certificate shall be issued to an Employee with respect to Stock purchased
hereunder until the expiration of eighteen (18) months from the date of exercise
of the Option to purchase such Stock. Nothing in this subsection (c) shall
prohibit the sale or other disposition by an Employee of shares of Stock
purchased hereunder. In the event the Company is required to obtain authority
from any commission or agency to issue any certificate or certificates for all
or a portion of the whole shares of Stock purchased hereunder, the Company shall
seek to obtain such authority as soon as reasonably practicable.

          (d)  Pro Rata Allocations. If the total number of shares of Stock for
which Options are to be exercised on any date exceeds the number of shares of
Stock remaining unsold under the Plan (after deduction for all shares of Stock
for which Options have theretofore been exercised), the Committee shall make a
pro rata allocation of the available remaining shares of Stock in as nearly a
uniform manner as shall be practicable and the balance of the amount credited to
the Account of each Employee which has not been applied to the purchase of
shares of Stock shall be paid to such Employee in one lump sum in cash within
thirty (30) days after the Date of Exercise, without any interest thereon.

          (e)  Information Statement. The Company shall provide each Employee
whose Option is exercised with an information statement in accordance with
Section 6039(a) of the Code and the Treasury Regulations thereunder. The Company
shall maintain a procedure for identifying certificates of shares of Stock sold
upon the exercise of Options in accordance with Section 6039(b) of the Code.

     5.   WITHDRAWAL FROM THE PLAN.

          (a)  Withdrawal Election. An Employee may withdraw from participation
under the Plan at any time, except that an Employee may not withdraw during the
last ten (10) days of any Option Period. An Employee electing to withdraw from
the Plan must deliver to the Company a notice of withdrawal in a form prepared
by the Committee (the "Withdrawal Election"), not later than ten (10) days prior
to the Date of Exercise for such Option Period. Upon receipt of an Employee's
Withdrawal Election, the Company or Subsidiary Corporation employing the
Employee shall pay to the Employee the amount credited to the Employee's Account
in one lump sum payment in cash, without any interest thereon, and subject to
Section 4(c), the Company shall (or shall cause the Agent to) deliver to the
Employee certificates for any whole shares of Stock previously purchased by the
Employee (the value of any fractional share to be returned to such Employee by
check), in either case within thirty (30) days of receipt of the Employee's
Withdrawal Election. Upon receipt of an Employee's Withdrawal Election by the
Company, the Employee shall cease to participate in the Plan and the Employee's
Option for such Option Period shall terminate.

                                       6

<PAGE>   9

          (b)  Eligibility following Withdrawal. An Employee who withdraws from
the Plan with respect to an Option Period, and who is still an Eligible
Employee, may elect to participate again in the Plan for any subsequent Offering
Period by delivering to the Company an Authorization pursuant to Section 3(b).

     6.   TERMINATION OF EMPLOYMENT.

          (a)  Termination of Employment Other than by Death. If the employment
of an Employee with the Company and the Subsidiary Corporation terminates other
than by death, the Employee's participation in the Plan automatically and
without any act on the Employee's part shall terminate as of the date of the
termination of the Employee's employment. As soon as practicable after such a
termination of employment, the Company or Subsidiary Corporation employing the
Employee shall pay to the Employee the amount credited to the Employee's Account
in one lump sum payment in cash, without any interest thereon, and subject to
Section 4(c), the Company shall (or shall cause the Agent to) deliver to the
Employee certificates for any whole shares of Stock previously purchased by the
Employee (the value of any fractional share to be returned to such Employee by
check). Upon an Employee's termination of employment covered by this subsection,
the Employee's Authorization and Option under the Plan shall terminate.

          (b)  Termination by Death. If the employment of an Employee is
terminated by the Employee's death, the executor of the Employee's will or the
administrator of the Employee's estate, by written notice to the Company, may
request payment of the balance in the Employee's Account, in which event the
Company or Subsidiary Corporation employing the Employee shall pay the amount
credited to the Employee's Account in one lump sum payment in cash, without any
interest thereon, and subject to Section 4(c), the Company shall (or shall cause
the Agent to) deliver to the Employee certificates for any whole shares of Stock
previously purchased by the Employee (the value of any fractional share to be
returned to such Employee by check) as soon as practicable after receiving such
notice. Upon receipt of such notice, the Employee's Authorization and Option
under the Plan shall terminate. If the Company does not receive such notice
prior to the next Date of Exercise, the Employee's Option shall be deemed to
have been exercised on such Date of Exercise.

     7.   RESTRICTION UPON ASSIGNMENT. An Option granted under the Plan shall
not be transferable other than by will or the laws of descent and distribution,
and is exercisable during the Employee's lifetime only by the Employee. Except
as provided in Section 6(b) hereof, an Option may not be exercised to any extent
except by the Employee. The Company shall not recognize and shall be under no
duty to recognize any assignment or alienation of the Employee's interest in the
Plan, the Employee's Option or any rights under the Employee's Option.

     8.   NO RIGHTS OF STOCKHOLDERS UNTIL SHARES ISSUED. With respect to shares
of Stock subject to an Option, an Employee shall not be deemed to be a
stockholder of the Company, and the Employee shall not have any of the rights or
privileges of a stockholder, until such shares have been issued to the Employee
or his or her nominee following exercise of the Employee's

                                       7

<PAGE>   10

Option. No adjustments shall be made for dividends (ordinary or extraordinary,
whether in cash securities, or other property) or distribution or other rights
for which the record date occurs prior to the date of such issuance, except as
otherwise expressly provided herein.

     9.   CHANGES IN THE STOCK AND CORPORATE EVENTS; ADJUSTMENT OF OPTIONS.

          (a)  Subject to Section 9(c), in the event that the Committee, in its
sole discretion, determines that any dividend or other distribution (whether in
the form of cash, Stock, other securities, or other property), recapitalization,
reclassification, stock split, reverse stock split, reorganization, merger,
consolidation, split-up, spin-off, combination, repurchase, liquidation,
dissolution, or sale, transfer, exchange or other disposition of all or
substantially all of the assets of the Company, or exchange of Stock or other
securities of the Company, issuance of warrants or other rights to purchase
Stock or other securities of the Company, or other similar corporate transaction
or event, affects the Stock 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 or with respect to an Option, then the
Committee shall, in such manner as it may deem equitable, adjust any or all of:

               (i)  the number and kind of shares of Stock (or other securities
          or property) with respect to which Options may be granted (including,
          but not limited to, adjustments of the limitation in Section 3(a) on
          the maximum number of shares of Stock which may be purchased),

               (ii) the number and kind of shares of Stock (or other securities
          or property) subject to outstanding Options, and

               (iii) the exercise price with respect to any Option.

          (b)  Subject to Section 9(c), in the event of any transaction or event
described in Section 9(a) or any unusual or nonrecurring transactions or events
affecting the Company, any affiliate of the Company, or the financial statements
of the Company or any affiliate, or of changes in applicable laws, regulations,
or accounting principles, the Committee, in its sole discretion, and on such
terms and conditions as it deems appropriate, either by the terms of the Option
or by action taken prior to the occurrence of such transaction or event and
either automatically or upon the Employee's request, is hereby authorized to
take any one or more of the following actions whenever the Committee determines
that such action is appropriate in order to prevent dilution or enlargement of
the benefits or potential benefits intended to be made available under the Plan
or with respect to any Option under the Plan, to facilitate such transactions or
events or to give effect to such changes in laws, regulations or principles:

               (i)  To provide that all Options outstanding shall terminate
          without being exercised on such date as the Committee determines in
          its sole discretion;

                                       8

<PAGE>   11

               (ii) To provide that all Options outstanding shall be exercised
          prior to the Date of Exercise of such Options on such date as the
          Committee determines in its sole discretion and such Options shall
          terminate immediately after such exercises.

               (iii) To provide for either the purchase of any Option
          outstanding for an amount of cash equal to the amount that could have
          been obtained upon the exercise of such Option had such Option been
          currently exercisable, or the replacement of such Option with other
          rights or property selected by the Committee in its sole discretion;

               (iv) To provide that such Option be assumed by the successor or
          survivor corporation, or a parent or subsidiary thereof, or shall be
          substituted for by similar options, covering the stock of the
          successor or survivor corporation, or a parent or subsidiary thereof,
          with appropriate adjustments as to the number and kind of shares and
          prices; and

               (v)  To make adjustments in the number and type of shares of
          Stock (or other securities or property) subject to outstanding
          Options, or in the terms and conditions of (outstanding Options, or
          Options which may be granted in the future.

          (c)  No adjustment or action described in this Section 9 or in any
other provision of the Plan shall be authorized to the extent that such
adjustment or action would cause the Plan to fail to satisfy the requirements of
Section 423 of the Code. Furthermore, no such adjustment or action shall be
authorized to the extent such adjustment or action would result in short-swing
profits liability under Section 16 of the Securities and Exchange Act of 1934,
as amended, or violate the exemptive conditions of Rule 16b-3 unless the
Committee determines that the Option is not to comply with such exemptive
conditions. The number of shares of Common Stock subject to any Option shall
always be rounded to the next whole number.

          (d)  The existence of the Plan and the Options granted hereunder shall
not affect or restrict in any way the right or power of the Company or the
stockholders of the Company to make or authorize any adjustment,
recapitalization, reorganization or other change in the Company's capital
structure or its business, any merger or consolidation of the Company, any issue
of stock or of options, warrants or rights to purchase stock or of bonds,
debentures, preferred or prior preference stocks whose rights are superior to or
affect the Stock or the rights thereof of which are convertible into or
exchangeable for Stock, or the dissolution or liquidation of the company, or any
sale or transfer of all or any part of its assets or business, or any other
corporate act or proceeding, whether of a similar character or otherwise.

     10.  USE OF FUNDS; NO INTEREST PAID. All funds received or held by the
Company under the Plan shall be included in the general funds of the Company
free of any trust or other restriction and may be used for any corporate
purpose. No interest will be paid to any Employee or credited to any Employee's
Account with respect to such funds.

                                       9

<PAGE>   12

     11.  DIVIDENDS.

          (a)  Cash dividends and other cash distributions received by the Agent
with respect to Stock held in its custody hereunder will be credited to each
Employee's Account in accordance with such Employee's interests in such Stock,
and shall be applied, as soon as practicable after the receipt thereof by the
Agent, to the purchase in the open market at prevailing market prices of the
number of whole shares of Stock that may be purchased with such funds (after
deductions of any bank service fees, brokerage charges, transfer taxes, and any
other transaction fee, expense or cost payable in connection with the purchase
of such shares of Stock and not otherwise paid by the Employer.)

          (b)  All purchases of shares of Stock made pursuant to this Section 11
will be made in the name of the Agent or its nominee, and shall be transferred
and credited to the Account(s) of the Employees to which such dividends or other
distributions were credited. Dividends paid in the form of shares of Stock will
be allocated by the Agent, as and when received, with respect to Stock held in
its custody hereunder to the Account of each Employee in accordance with such
Employee's interests in such Stock. Property, other than Stock or cash, received
by the Agent as a distribution on Stock held in its custody hereunder, shall be
sold by the Agent for the accounts of Employees, and the Agent shall treat the
proceeds of such sale in the same manner as cash dividends received by the Agent
on Stock held in its custody hereunder.

     12.  AMENDMENT, SUSPENSION OR TERMINATION OF THE PLAN. The Board may amend,
suspend, or terminate the Plan at any time and from time to time, provided that
approval by a vote of the holders of the outstanding shares of the Company's
capital stock entitled to vote shall be required to amend the Plan to: (a)
change the number of shares of Stock that may be sold pursuant to Options under
the Plan, (b) alter the requirements for eligibility to participate in the Plan,
or (c) in any manner that would cause the Plan to no longer be an "employee
stock purchase plan" within the meaning of Section 423(b) of the Code.

     13.  ADMINISTRATION BY COMMITTEE; RULES AND REGULATIONS.

          (a)  Appointment of Committee. The Plan shall be administered by the
Committee, which shall be composed of not less than two members of the Board,
each of whom shall be a "non-employee director" within the meaning of Rule 16b-3
which has been adopted by the Securities and Exchange Commission under the
Securities Exchange Act of 1934, as amended. Each member of the Committee shall
serve for a term commencing on a date specified by the Board and continuing
until the member dies, resigns or is removed from office by the Board. The
Committee at its option may utilize the services of an agent to assist in the
administration of the Plan, including establishing and maintaining an individual
securities account under the Plan for each Employee.

          (b)  Duties and Powers of Committee. It shall be the duty of the
Committee to conduct the general administration of the Plan in accordance with
the provisions of the Plan. The Committee shall have the power to interpret the
Plan and the terms of the Options and to adopt such rules for the
administration, interpretation, and application of the Plan as are consistent

                                       10

<PAGE>   13

therewith and to interpret, amend or revoke any such rules. In its absolute
discretion, the Board may at any time and from time to time exercise any and all
rights and duties of the Committee under the Plan.

          (c)  Majority Rule. The Committee shall act by a majority of its
members in office. The Committee may act either by vote at a meeting or by a
memorandum or other written instrument signed by a majority of the Committee.

          (d)  Compensation; Professional Assistance; Good Faith Actions. All
expenses and liabilities incurred by members of the Committee in connection with
the administration of the Plan shall be borne by the Company. The Committee may,
with the approval of the Board, employ attorneys, consultants, accountants,
appraisers, brokers or other persons. The Committee, the Company and its
officers and directors shall be entitled to rely upon the advice, opinions or
valuations of any such persons. All actions taken and all interpretations and
determinations made by the Committee in good faith shall be final and binding
upon all Employees, the Company and all other interested persons. No member of
the Committee shall be personally liable for any action, determination or
interpretation made in good faith with respect to the Plan or the Options, and
all members of the Committee shall be fully protected by the Company in respect
to any such action, determination, or interpretation.

     14.  DESIGNATION OF SUBSIDIARY CORPORATIONS. The Board shall designate from
among the Subsidiary Corporations, as determined from time to time, the
Subsidiary Corporation or Subsidiary Corporations whose Employees shall be
eligible to be granted Options under the Plan. The Board may designate a
Subsidiary Corporation, or terminate the designation of a Subsidiary
Corporation, without the approval of the stockholders of the Company.

     15.  NO RIGHTS AS AN EMPLOYEE. Nothing in the Plan shall be construed to
give any person (including any Eligible Employee) the right to remain in the
employ of the Company, a Parent Corporation or a Subsidiary Corporation or to
affect the right of the Company, any Parent Corporation or any Subsidiary
Corporation to terminate the employment of any person (including any Eligible
Employee) at any time, with or without cause.

     16.  TERM; APPROVAL BY STOCKHOLDERS. Subject to approval by the
stockholders of the Company in accordance with this Section, the Plan shall be
in effect until May 1, 2010, unless sooner terminated in accordance with Section
12. No Option may be granted during any period of suspension of the Plan or
after termination of the Plan. The Plan shall be submitted for the approval of
the Company's stockholders within twelve (12) months after the date of the
adoption of the Plan by the Board. Options may be granted prior to such
stockholder approval; provided, however, that such Options shall not be
exercisable prior to the time when the Plan is approved by the Company's
stockholders; and, provided, further, that if such approval has not been
obtained by the end of said 12-month period, all Options previously granted
under the Plan shall thereupon terminate without being exercised.

     17.  EFFECT UPON OTHER PLANS. The adoption of the Plan shall not affect any
other compensation or incentive plans in effect for the Company, any Parent
Corporation or any

                                       11

<PAGE>   14

Subsidiary Corporation. Nothing in this Plan shall be construed to limit the
right of the Company, any Parent Corporation or any Subsidiary Corporation to:
(a) establish any other forms of incentives or compensation for employees of the
Company, any Parent Corporation or any Subsidiary Corporation or (b) grant or
assume options otherwise than under the Plan in connection with any proper
corporate purpose, including, but not by way of limitation, the grant or
assumption of options in connection with the acquisition, by purchase, lease,
merger, consolidation or otherwise, of the business, stock or assets of any
corporation, firm or association.

     18.  CONDITIONS TO ISSUANCE OF STOCK CERTIFICATES. The Company shall not be
required to issue or deliver any certificate or certificates for shares of Stock
purchased upon the exercise of Options prior to fulfillment of all the following
conditions:

          (a)  The admission of such shares to listing on all stock exchanges,
if any, on which is then listed; and

          (b)  The completion of any registration or other qualification of such
shares under any state or federal law or under the rulings or regulations of the
Securities and Exchange Commission or any other governmental regulatory body,
which the Committee shall, in its absolute discretion, deem necessary or
advisable; and

          (c)  The obtaining of any approval or other clearance from any state
or federal governmental agency which the Committee shall, in its absolute
discretion, determine to be necessary or advisable; and

          (d)  The payment to the Company of all amounts which it is required to
withhold under federal, state or local law upon exercise of the Option; and

          (e)  The lapse of such reasonable period of time following the
exercise of the Option as the Committee may from time to time establish for
reasons of administrative convenience.

     19.  NOTIFICATION OF DISPOSITION. Each Employee shall give prompt notice to
the Company of any disposition or other transfer of any shares of Stock
purchased upon exercise of an Option if such disposition or transfer is made:
(a) within two (2) years from the Date of Grant of the Option, or (b) within one
(1) year after the transfer of such shares of Stock to such Employee upon
exercise of such Option. Such notice shall specify the date of such disposition
or other transfer and the amount realized, in cash, other property, assumption
of indebtedness or other consideration, by the Employee in such disposition or
other transfer.

     20.  NOTICES. Any notice to be given under the terms of the Plan to the
Company shall be addressed to the Company in care of its Secretary and any
notice to be given to any Employee shall be addressed to such Employee at such
Employee's last address as reflected in the Company's records. By a notice given
pursuant to this Section, either party may designate a different address for
notices to be given to it, him or her. Any notice which is required to be

                                       12

<PAGE>   15

given to an Employee shall, if the Employee is then deceased, be given to the
Employee's personal representative if such representative has previously
informed the Company of his status and address by written notice under this
Section. Any notice shall have been deemed duly given if enclosed in a properly
sealed envelope or wrapper addressed as aforesaid at the time it is deposited
(with postage prepaid) in a post office or branch post office regularly
maintained by the United States Postal Service.

                                       13

<PAGE>   16

     21.  HEADINGS. Headings are provided herein for convenience only and are
not to serve as a basis for interpretation or construction of the Plan.

                                  * * * * * * *

     I hereby certify that the ACLARA BioSciences, Inc. Employee Stock Purchase
Plan was adopted by the Board of Directors of ACLARA BioSciences, Inc. on
February 11, 2000.

     Executed at Mountain View, California on this ___th day of _______, 2000.

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

                                       -----------------------------------------
                                       Secretary

                                  * * * * * * *

     I hereby certify that the ACLARA BioSciences, Inc. Employee Stock Purchase
Plan was approved by the stockholders of ACLARA BioSciences, Inc. on
_________________, 2000.

     Executed at Mountain View, California on this ___th day of _______, 2000.

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

                                       -----------------------------------------
                                       Secretary

                                       14

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