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                                                                   EXHIBIT 10.27

      AMENDMENT TO THE CUSTOM INSTRUMENT DEVELOPMENT AND COMMERCIALIZATION
   AGREEMENT BETWEEN THE R. W. JOHNSON PHARMACEUTICAL RESEARCH INSTITUTE, ABI
             APPLIED BIOSYSTEMS GROUP, AND ACLARA BIOSCIENCES, INC.




     This amendment to the Custom Instrument Development and Commercialization
Agreement (the "Amendment"), signed by the Parties as of October 1, 2001 (the
"Amendment Signing Date"), and effective as of September 30, 2000 (the
"Amendment Effective Date"), is by and between The R. W. Johnson Pharmaceutical
Research Institute, a division of Ortho-McNeil Pharmaceutical, Inc., a Delaware
corporation having a business address at 920 U.S. Route 202, Raritan, New Jersey
(hereinafter "PRI"), Applied Biosystems Group, a business of PE Corporation (NY)
having a principal place of business at 850 Lincoln Center Drive, Foster City,
California 94404 (hereinafter "ABG") and ACLARA BioSciences, Inc., a Delaware
corporation having a principal place of business at 1288 Pear Avenue, Mountain
View California 94043-1432 (hereinafter "ACLARA"). PRI, ABG, and ACLARA are
referred to in this Amendment individually or collectively as Party or Parties,
as the case may be.

                                   BACKGROUND

     The Parties entered into the Custom Instrument Development and
Commercialization Agreement, dated October 1, 1998 (the "PRI Agreement"),
pursuant to which the Parties pursued the goal of designing, developing and
producing prototype high-throughput chip reading devices incorporating
microfluidic technology .

     PRI and ACLARA desire to continue collaborative research under the PRI
Agreement after the Amendment Effective Date, and desire to modify certain
aspects of the PRI Agreement in order to continue the collaborative research
initiated under the PRI Agreement.

     ABG wishes to withdraw from further participation in collaborative research
under the PRI Agreement as of the Amendment Effective Date.

     NOW, THEREFORE, in consideration of the above premises and the covenants
set forth in this Amendment, the PRI Agreement shall be and hereby is amended so
that, on and after the Amendment Effective Date, the agreement between the
parties with respect to the subject matter of the PRI Agreement shall be the
terms and conditions set forth in the PRI Agreement as modified in this
Amendment.

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                                    AGREEMENT

     1. "PE" shall be deleted and replaced by "ABG" throughout the PRI
Agreement. ABG shall have the same meaning in the PRI Agreement as defined in
this Amendment.

     2. On the Amendment Effective Date and thereafter, PRI and ACLARA shall
release, and hereby do release, ABG from all covenants, promises, undertakings,
duties and responsibilities of further performance under the PRI Agreement,
except as otherwise provided herein.

     3. On the Amendment Effective Date and thereafter, ABG shall release, and
hereby does release, PRI from all covenants, promises, undertakings, duties and
responsibilities of further performance under the PRI Agreement, to the extent
that such further performance is an obligation of PRI to ABG under the PRI
Agreement, and except as otherwise provided herein.

     4. On the Amendment Effective Date and thereafter, ABG shall release, and
hereby does release, ACLARA from all covenants, promises, undertakings, duties
and responsibilities of further performance under the PRI Agreement, to the
extent that such further performance is an obligation of ACLARA to ABG under the
PRI Agreement, and except as otherwise provided herein.

     5. On the Amendment Effective Date and thereafter and except as otherwise
provided herein, ACLARA shall assume responsibility, and hereby assumes
responsibility, for performing all covenants, promises, undertakings, and duties
assigned to ACLARA solely, ABG solely, or to ABG and ACLARA jointly, under the
PRI Agreement.

     6. On the Amendment Effective Date and thereafter, ABG shall convey,
transfer and assign, and hereby conveys, transfers and assigns, all of its
rights under the PRI Agreement to ACLARA, regardless of whether ABG holds such
rights solely, or jointly with ACLARA, or jointly with any other entity.

     7. Notwithstanding any other provision of this Amendment, ABG, ACLARA, and
PRI shall remain bound by the confidentiality obligations and covenants of
Article 10 of the PRI Agreement, such Article 10 entitled "Confidentiality."

     8. All other provisions of the PRI Agreement not expressly modified by this
Amendment shall remain in full force and effect.

[Signature page follows.]


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     IN WITNESS WHEREOF, this Amendment has been entered into by and between
ABG, ACLARA and PRI by their respective duly authorized representatives as of
the Amendment Effective Date.

APPLIED BIOSYSTEMS GROUP OF               ACLARA BIOSCIENCES, INC.

PE CORPORATION (NY)


By: /s/ Michael W. Hunkapiller            By: /s/ Joseph M. Limber
    ----------------------------------        ----------------------------------

Name: Michael W. Hunkapiller              Name: Joseph M. Limber
     ---------------------------------         ---------------------------------

Title: President, Applied Biosystems      Title: President, CEO
       Group, Executive Vice                    --------------------------------
       President, PE Corporation
      --------------------------------

Date: October 8, 2001                     Date: October 15, 2001
     ---------------------------------         ---------------------------------



THE R. W. JOHNSON PHARMACEUTICAL
RESEARCH INSTITUTE, INC., A DIVISION
OF ORTHO-McNEIL PHARMACEUTICAL,
INC.

By: /s/ Michael R. Jackson, Ph.D.
   -----------------------------------

Name: Michael R. Jackson, Ph.D.
     ---------------------------------

Title: Sr. V.P. Drug Discovery
      --------------------------------

Date: October 5, 2001
     ---------------------------------


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