<PAGE>


                                                            EXHIBIT NO. 10.43



  Confidential Materials omitted and filed separately with the Securities and
             Exchange Commission. Asterisks denote such omissions.

                                    AGREEMENT

          PFIZER INC, a Delaware corporation, with an address at 235 East 42nd
          Street, New York, NY 10017 and its Affiliates ("Pfizer"), and
          GENAISSANCE PHARMACEUTICALS, INC. with an address at Five Science
          Park, New Haven, CT 06511 and its Affiliates ("Genaissance"), enter
          into this Agreement for the determination of genetic variation and
          haplotypic information of genes on the following terms and conditions:

1.        DEFINITIONS: Whenever used in this Agreement, the terms defined in
          this Section 1 shall have the meanings specified.

1.1       "Affiliate" means any corporation, firm, partnership or other entity
          which directly or indirectly controls, is controlled by, or is under
          common control with either of the parties.

1.2       "Pfizer Gene List" shall mean a gene or genes listed in Appendix 1 to
          Exhibit A, as amended from time to time, requested by Pfizer for
          testing by Genaissance according to the Research Plan.

1.3       "Research Plan" shall mean the written plan describing the research to
          be carried out by Genaissance. The Research Plan is appended to and
          made a part of this Agreement as Exhibit A.

1.4       "Results" shall mean all information relating to the Pfizer Gene List
          generated according to the Research Plan.

2.        SCOPE OF WORK: Genaissance will complete the Research Plan within the
          time period set forth therein.

3.        TERM: The term of this Agreement is one (1) year from August 31, 2001.

4.        PAYMENT: Pfizer will pay Genaissance, pursuant to the cost structure
          set forth in Exhibit A, within [**] of receipt of
          Genaissance's invoice for work performed and receipt of a final report
          pursuant to Section 11. All invoices shall be sent to Mrs. Sue
          Milroy, Pfizer Limited, Ramsgate Road, Sandwich, Kent CT13 9NJ,
          England.

5.        INTELLECTUAL PROPERTY: Genaissance acknowledges that Pfizer will make
          and use the Results as it sees fit in the development or
          commercialization of pharmaceutical products without further
          compensation to Genaissance.

<PAGE>

          With that exception, neither party licenses or conveys intellectual
          property of any kind to the other.

6.        INFORMATION: For purposes of this Agreement, the term "Information"
          will mean the Pfizer Gene List, the Research Plan and all written
          information relating to the Pfizer Gene List, the Research Plan, data,
          know-how, technical and non-technical materials which Pfizer may
          deliver to Genaissance pursuant to this Agreement, stamped
          "Confidential," and all oral material which Pfizer declares to be
          confidential and confirm such declaration in writing within thirty
          (30) days of disclosure. Information shall not include any Results
          generated by Genaissance pursuant to this Agreement.

7.        CONFIDENTIALITY: Genaissance agrees to maintain the Information in
          confidence with the same degree of care it holds its own confidential
          information. Genaissance will not use the Information except to
          perform the Research Plan. Genaissance will disclose the Information
          only to its officers and employees directly concerned with the
          Research Plan, but will neither disclose the Information to any third
          party nor use the Information for any other purpose.

8.        EXCEPTION TO CONFIDENTIALITY: Genaissance's obligation of
          non-disclosure and the limitations upon the right to use the
          Information will not apply to the extent that it can demonstrate that
          the Information a) was in its possession prior to the time of
          disclosure by Pfizer; or b) is or becomes public knowledge through no
          fault or omission of Genaissance; or c) is obtained by Genaissance
          from a third party under no obligation of confidentiality to Pfizer;
          or d) if Genaissance is requested to disclose Information in
          connection with a legal or administration proceeding, Genaissance will
          give Pfizer prompt notice of such request. If Pfizer attempts and
          fails to obtain a protective order or waive compliance with the
          relevant provisions of this Agreement, Genaissance will disclose only
          that portion of Information which its legal counsel determines it is
          required to disclose.

9.        SURVIVAL OF CONFIDENTIALITY OBLIGATION: All confidentiality
          obligations of Genaissance under this Agreement will survive the
          termination of this Agreement for a period of five (5) years.

10.       PUBLICITY: No press releases or other statements in connection with
          this Agreement intended for use in the public or private media shall
          be made by Pfizer or Genaissance without the prior written consent of
          the other party; provided, however that Pfizer shall have the right
          to publish the results, provided such manuscript is submitted to
          Genaissance for review prior to publication. No right of manuscript
          approval by Genaissance is implied by this provision. If either
          party is required by law or governmental regulation to describe its
          relationship to the other, it shall promptly give the other party
          notice with a copy of any disclosure it proposes to make. In
          addition, neither party shall use the other party's name in
          connection with any instruments, products, promotion, or advertising
          without prior written permission of the other party.

11.       REPORT: Genaissance will provide to Pfizer a written report containing
          Results regarding each gene within thirty (30) days following
          completion of the Research Plan for such gene(s), detailing the work
          performed.

<PAGE>


12.       INDEMNIFICATION: Pfizer will defend, indemnify and hold harmless
          Genaissance, its employees, directors and officers, from and against
          any and all liability which it may incur by reason of Pfizer's use of
          the Results. Genaissance will indemnify Pfizer, its employees,
          consultants, directors and officers for any claims for injuries to
          persons or damages which occur on Genaissance's premises or premises
          under the control of Genaissance.

13.       ENTIRE AGREEMENT: This Agreement, together with all exhibits attached
          hereto, and set forth the entire agreement between Pfizer and
          Genaissance as to its subject matter. None of the terms of this
          Agreement shall be amended except in writing signed by both parties.

14.       BREACH: If either party breaches this Agreement, the other may
          terminate it if the breaching party does not cure the breach within
          thirty (30) days of written notice of the same. The right of
          termination shall be in addition to any other rights the terminating
          party may have, at law or equity, pursuant to this Agreement.

15.       FORCE MAJEURE: Neither Pfizer nor Genaissance shall be liable for
          failure of or delay in performing obligations set forth in this
          Agreement, and neither shall be deemed in breach of its obligations,
          if such failure or delay is due to natural disasters or any causes
          reasonably beyond control of Pfizer or Genaissance.

16.       CHOICE OF LAW: This Agreement shall be construed in accordance with
          the laws of the State of New York.



      GENAISSANCE
      PHARMACEUTICALS, INC.                                   PFIZER INC.

By: /S/ KRISHNAN NANDABALAN                         By:   /S/ ALAN R. PROCTOR
    ----------------------------                       ------------------------
Name: Krishnan Nandabalan, Ph.D.                    Name:  Alan R. Proctor
                                                         ----------------------
Title: Vice President, Alliances                    Title: Vice President,
                                                           Strategic Alliances
                                                          ---------------------
Date: AUGUST 29, 2001                               Date:  AUGUST 29, 2001
      ---------------                                    ----------------------

cc:  Pfizer Inc., Legal Division, Groton, CT  06340

<PAGE>


                                    EXHIBIT A

                                    PROPOSAL

PFIZER/GENAISSANCE: A PROPOSAL FOR COMPREHENSIVE SNP IDENTIFICATION IN CANDIDATE
GENES

[**]

RESEARCH GOAL: To define comprehensive genetic variation and haplotype
information in key candidate genes of research interest to PGRD (Pfizer, please
define this acronym).

RESEARCH PROPOSAL

o         Pfizer will provide Genassiance with [**] approximately [**]
          candidate genes (see Appendix 1 for details) for which Genaissance
          will obtain a comprehensive assessment of genetic variation.

          Genaissance will provide genomic sequence for the candidate genes
          listed in Appendix 1. This sequence will be generated using
          Genaissance's Standard Operating Procedure for discovering HAP(TM)
          Markers for a gene. This procedure consists of sequencing, from the
          Index Repository, ninety-three (93) individual samples of human
          genomic DNA and one sample of chimpanzee genomic DNA. The genomic
          regions of each gene, which are targeted for sequencing, are as
          follows.

          (vi)   "Exons" shall mean the genomic DNA segments of a gene whose
          sequence information is translated into the protein product of that
          gene. The goal is to obtain sequence information for all Exons
          of a gene.

          (vii)  "Exon/Intron Junction" shall mean the junctions between the
          Exons and the Introns in genomic DNA. Beginning with the initiation
          codon at one end of a gene and ending with the termination codon at
          the other end of a gene, the goal is to obtain sequence information
          for each Exon/Intron Junction within this genomic region.

          (viii)  "Introns" shall mean the genomic DNA segments of a gene
          which are located between Exons. Beginning with the initiation codon
          at one end of a gene and ending with the termination codon at
          the other end of a gene, the goal is to obtain a minimum of ten (10)
          to twenty (20) bases and a maximum of one hundred (100) bases of
          sequence information from the Exon/Intron Junction into the Intron
          for every Intron within this genomic region.

          (ix)   "Promoter" shall mean the region that is immediately
          upstream of the genomic segment that is found at the five-prime
          end of a Messenger RNA molecule. ("Messenger RNA" shall mean a
          ribonucleic acid sequence from which the protein product of a gene
          is translated.) The goal is to obtain sequence information for up
          to one thousand (1000) bases of the Promoter, with the desire to
          obtain an addition 1 KB where possible.

          (x)    "Three-Prime Untranslated Region" shall mean the genomic
          region immediately downstream from the termination codon of a gene.
          The goal is to obtain sequence information for at least one hundred
          (100) bases of the Three-Prime Untranslated Region downstream of
          the Three-Prime Untranslated Region downstream of the termination
          codon. Optimally, we will have coverage of 500 bases of the 3' UTR.

               Specific genomic information is required to meet the goals
          outlined in (i) through (v) above. If genomic sequence information
          is available for a majority of these regions, even if the available
          genomic sequence information is not sufficient to meet all of the
          goals in (i) through (v) above, a gene will still be queued for
          HAP(TM) Marker discovery.

<PAGE>


          (v)   "Three-Prime Untranslated Region" shall mean [**]. The goal
          is to obtain sequence information [**] optimally, we will have [**].

                Specific genomic sequence information is required to meet the
          goals outlined in (i) through (v) above. If genomic sequence
          information is available for a majority of these regions, even if the
          available genomic sequence information is not sufficient to meet all
          of the goals in (i) through (v) above, [**].

o         A gene shall be considered completely sequenced if sequence
          information is obtained for: (i) at least [**] of the [**];
          (ii) the [**] containing the [**]; and (iii) [**]. A
          specific region targeted for sequencing within a gene shall be
          considered completely sequenced if sequence information is obtained
          for at least [**] individuals from the Index Repository. However, the
          presence of runs of guanine and cytosine, secondary structure or
          errors in publicly available sequence information may prevent the
          generation of sufficient sequence information for that gene to be
          considered completely sequenced as defined above.

o         The candidate genes will be interrogated using Genaissance's SNP
          Scoring and HAP(TM) Building Standard Operating Procedures for
          identification of SNPs and inference of haplotypes.

o         The results of performing the above Standard Operating Procedures for
          each gene will be reported [**] and will [**] in which [**].

o         Genaissance shall complete the foregoing Research Proposal for the
          initial list of [**] genes within approximately [**] of receipt
          [**].


<PAGE>


COST STRUCTURE

Payment is based upon the cost per gene, as set forth below. A minimum of [**]
genes will be analyzed within one calendar year from the commencement of the
collaboration.


Costs:
[**]
[**]
[**]



              PFIZER GENE LIST FOR COMPREHENSIVE VARIANT DETECTION

<TABLE>
<CAPTION>
-------------------- ---------------- ------------------ -----------------------
GENE                 SYMBOL           LOCATION           GENBANK ACC NO
-------------------- ---------------- ------------------ -----------------------
<S>                 <C>              <C>                <C>

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

-------------------- ---------------- ------------------ -----------------------
                                     [**]
-------------------- ---------------- ------------------ -----------------------

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

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</TABLE>