<PAGE>

                                                                   EXHIBIT 10.23

                         SEQUENOM BETA TEST AGREEMENT

This Agreement, dated July 15, 1999, is made by and between SEQUENOM, Inc., a
corporation with its principal place of business located at 11555 Sorrento
Valley Rd, San Diego, CA, 92121-1331, ("Company"), and Genzyme Corporation, a
corporation with its place of business at One Mountain Road, P.O. Box 9322,
Framingham, MA, 01701-9322 ("Recipient").

     WHEREAS, Company is willing to supply within the protection of a
confidential relationship, the DNA MassArray(TM) system and related materials
listed on Schedule A attached hereto ("Evaluation Item") to Recipient by the
week of August 16, 1999 solely for evaluating whether to enter full commercial
business arrangement with the Company ("Evaluation");

     WHEREAS, Recipient desires to have access to the Evaluation Item and is
aware of the nature of the Evaluation Item, and is willing to enter a
confidential relationship and to use and test the Evaluation Item and report to
Company on a confidential basis the performance of the Evaluation Item;

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
hereinafter set forth, the parties hereby agree as follows:

     1.   Use of DNA MassArray(TM) and SpectroChip(TM) License. Subject to the
          ----------------------------------------------------
terms of this Agreement, Company grants to Recipient            ***
nonsublicensable, nonexclusive license to use the Evaluation Item    *** during
the term of this Agreement unless explicitly agreed to in writing by the
Company. The Company shall at all times retain all title to and ownership of the
Evaluation Item and all ancillary products thereof. Recipient agrees to use the
Evaluation Item only in the ordinary course of testing, and Recipient will not
reproduce or modify the Evaluation Item or any portion thereof. Recipient shall
not rent, sell, lease or otherwise transfer the Evaluation Item or any part
thereof or use it for the benefit of a third party. Recipient shall not reverse
assemble, reverse compile or reverse engineer the Evaluation Item, or otherwise
attempt to discover any Evaluation Item underlying Proprietary Information (as
that term is defined below).

     2.   Business Terms. All fees herein are for the use of Company's
          --------------
Evaluation Item and the services required for the operation of the Evaluation
Item including training and support.


i.        ***  for the Company's Evaluation Item for the first six months after
the initiation of the first test. After the completion of the initial 6-month
Beta-test period, Recipient may purchase the Evaluation Item for       ***   .

ii.       ***  fee during the Beta-test period for all tests performed for the
     objective evaluation of the Evaluation Item and/or the comparison of
     Evaluation Item with other DNA analysis methods and with results of
     evaluation and comparison tests (other than patient information) reported
     to SEQUENOM on a confidential basis. All samples being



     *** Portions of this page have been omitted pursuant to a request for
Confidential Treatment and filed separately with the Commission.

Confidential                       Page 1
<PAGE>

Beta Test Agreement

     analyzed using the Evaluation Item for testing other than for the purposes
     as set forth in the preceding sentence shall have an Element fee of ***
     (the "Element Fee"); An "Element" represents one BiomassPROBE reaction
     unit (Patent US 5,605,798) on Company's SpectroChip(TM) and includes the
     reaction unit and reagents necessary to characterize a PCR product for SNP
     analysis.

iii. A Maintenance Fee that includes Evaluation Item Support and Company
     Bioinformatics Workstation updates ("Maintenance") of     ***     ***
     ***. Evaluation Item Maintenance shall include installation, training,
     ongoing maintenance and support for the term of the Evaluation provided by
     the Company. The Maintenance Fee is strictly for this Evaluation Item
     during the evaluation period. Pricing of a maintenance fee on any future
     agreements would be dependent on the nature of that agreement.

     3.  Confidentiality; Ownership. Recipient acknowledges that, in the course
         --------------------------
of using the Evaluation Item and performing its duties under this Agreement, it
may obtain information relating to the Evaluation Item and/or Company ("Company
Proprietary Information").  Such Company Proprietary Information shall belong
solely to Company and includes, but is not limited to, the existence of the
Evaluation Item, its features and mode of operation, this Agreement, trade
secrets, know-how, inventions (whether or not patentable), techniques,
processes, programs, ideas, algorithms, schematics, testing procedures, software
design and architecture, computer code, internal documentation, design and
function specifications, product requirements, problem reports, analysis and
performance information, software documents, and other technical, business,
product, marketing and financial information, plans and data.

     Company acknowledges that, in the course of the Recipient using the
Evaluation Item and performing its duties under this Agreement, it may obtain
information relating to the Recipient's assays and/or the Recipient ("Recipient
Proprietary Information"). Such Recipient Proprietary Information shall belong
solely to Recipient and includes, but is not limited to the existence of such
assays, any know-how, techniques, processes, and other recipient specific
technical, business, product, marketing and financial information, plans, and
data. Further, Recipient shall own all discoveries, inventions, (whether or not
patentable), data and other results arising from the use of the Recipient's
***    with the Evaluation Item, but only to the extent that such discovery,
invention, data or results relates to the use and operation of Recipient's
***     and Recipient expressly reserves all intellectual property rights
therein with the exception of those enumerated in Paragraph 3 (d) below.


     In regard to both Company and Recipient ("Parties") Proprietary
Information:

          (a) Parties shall not, during the term of this Agreement, and for a
          period of at least three (3) years after its termination, use (except
          as expressly authorized by this Agreement) or disclose Proprietary
          Information without the prior written consent of the other party
          unless such Proprietary Information becomes part of the public


     *** Portions of this page have been omitted pursuant to a request for
Confidential Treatment and filed separately with the Commission.

Confidential                       Page 2
<PAGE>

Beta Test Agreement

          domain without breach of this Agreement by either party, its officers,
          directors, employees or agents.

          (b) During the period specified in (a) above, both parties agree to
          take all reasonable measures to maintain the Proprietary Information
          and Evaluation Item in confidence.

          (c) During the period specified in (a) above, both Parties will
          disclose the Evaluation Item and Proprietary Information only to those
          of its employees and consultants as are necessary for the use
          expressly and unambiguously licensed hereunder, provided such
          employees and contractors are subject to confidentiality obligations
          consistent with those set forth herein. Recipient shall not, without
          the prior written consent of Company, disclose or otherwise make
          available the Evaluation Item or any ancillary products to any third
          party.

          (d) Recipient hereby assigns to Company any invention, improvement,
          idea or know-how (whether or not patentable) that is conceived,
          learned or reduced to practice in the course of performance under this
          Agreement, but only to the extent that such invention, idea, or know-
          how relates to the use and operation of the Evaluation Item and any
          patent rights, trade secret rights, mask work rights, sui generis
          database rights and all other intellectual and industrial property
          rights of any sort with respect thereto. Recipient agrees to take any
          action reasonably requested by Company to evidence, perfect, obtain,
          or maintain the foregoing.

     4.  Reports. A Company senior scientist, assisted by Recipient, shall
         -------
provide written reports monthly commencing after the date of the first test at
the Recipient's facility. Reports shall disclose: (1) which portions of the
Evaluation Item have been used, (2) the nature of that use, (3) the extent or
amount of use, (4) all errors or difficulties discovered, (5) suggestions on
improving the Evaluation Item, (6) the characteristic conditions and symptoms of
the errors and difficulties, in sufficient detail to allow the Company to
recreate the errors and difficulties itself, and (7) a performance comparison
with other available systems and methods in use at the Recipients facility,
including but not limited to, accuracy, time of assay, repeat tests performed
and instrument down-time.

     5.  WARRANTY DISCLAIMER. The parties acknowledge that the Evaluation Item
         -------------------
is for use in a Beta test. COMPANY DISCLAIMS ALL WARRANTIES RELATING TO THE
EVALUATION ITEM, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, ANY
WARRANTIES AGAINST INFRINGEMENT OF THIRD-PARTY RIGHTS, MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE.

     6.  Limitation of Remedies and Damages. COMPANY SHALL NOT BE RESPONSIBLE OR
         ----------------------------------
LIABLE WITH RESPECT TO ANY SUBJECT MATTER OF THIS AGREEMENT UNDER ANY CONTRACT,
NEGLIGENCE, STRICT LIABILITY OR OTHER THEORY (A) FOR LOSS OR INACCURACY OF DATA
OR COST OF PROCUREMENT OF SUBSTITUTE GOODS, SERVICES OR TECHNOLOGY, OR (B) FOR
ANY INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES INCLUDING, BUT

Confidential                       Page 3
<PAGE>

Beta Test Agreement

NOT LIMITED TO LOSS OF REVENUES AND LOSS OF PROFITS. COMPANY SHALL NOT BE
RESPONSIBLE FOR ANY MATTER BEYOND ITS REASONABLE CONTROL.

     7.  Nonassignability. Neither the rights nor the obligations arising under
         ----------------
this Agreement are assignable or transferable by Recipient, and any such
attempted assignment or transfer shall be void and without effect.

     8.  Execution of Agreement, Controlling Law. Attorneys' Fees and
         ------------------------------------------------------------
Severability. This Agreement shall become effective only upon its execution by
------------
both Company and Recipient and it shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts without regard to
the conflicts of laws provisions therein. In the event that any of the
provisions of this Agreement shall be held by a court or other tribunal of
competent jurisdiction to be unenforceable, such provisions shall be limited or
eliminated to the minimum extent necessary so that this Agreement shall
otherwise remain in full force and effect and enforceable.

     9. Entire Agreement. This Agreement constitutes the entire agreement
        ----------------
between the parties pertaining to the subject matter hereof, and any and all
written or oral agreements previously existing between the parties are expressly
canceled with the exception of any prior Confidentiality Agreement executed
between the two Parties. Any modifications of this Agreement must be in writing
and signed by both parties.

     10.  Equitable Relief. Recipient acknowledges and agrees that due to the
          ----------------
unique nature of Company's Proprietary Information, there may be no adequate
remedy at law for any breach of its obligations hereunder, that any such breach
may allow Recipient or third parties to unfairly compete with Company resulting
in irreparable harm to Company, and therefore, upon any such breach or threat
thereof, Company shall be entitled to seek injunctions and other appropriate
equitable relief in addition to whatever remedies it may have at law.

     11.  Termination. This Agreement maybe terminated by Company or Recipient
          -----------
for any reason or no reason upon twenty-one (21) days' written notice to the
other party at its address listed above, or immediately upon notice of any
breach by either party of the provisions of this Agreement that has not been
cured within 10 days, and in any case will terminate six (6) months after the
initiation of the Evaluation at the Recipient's facility. Upon termination, all
payments owing Company up to the point of the date of termination shall be due
within thirty (30) days of the termination date and the license granted
hereunder shall terminate and Recipient shall immediately return the Evaluation
Item, together with any and all documents, notes and other materials regarding
the Evaluation Item to Company, including, without limitation, all Proprietary
Information and all copies and extracts of the foregoing, but the terms of this
Agreement, excluding Paragraph 2 will otherwise remain in effect.

     Company and Recipient will enter into good faith discussions sixty (60)
days prior to the termination of the Beta Site Agreement to either extend the
current Agreement or negotiate a full DNA MassArray(TM) license Agreement.



Confidential                       Page 4
<PAGE>

Beta Test Agreement

     12.  Public Announcements. Any announcements or similar publicity with
          --------------------
respect to the execution of this Agreement shall be agreed upon between the
Parties in advance of such announcement. Both Parties understand that this
Agreement is likely to be of significant interest to investors, analysts and
others, and that the Parties therefore may make such public announcements with
respect thereto. The Parties agree that any such announcement will not contain
confidential business or technical information and, if disclosure of
confidential business or technical information is required by law or regulation,
will make reasonable efforts to minimize such disclosure and obtain confidential
treatment for any such information which is disclosed to a governmental agency
or group. Each Party agrees to provide to the other Parties a copy of any public
announcement as soon as reasonably practicable under the circumstances prior to
its scheduled release. Except under extraordinary circumstances, each Party
shall provide the other with an advance copy of any press release at least five
(5) business days prior to the scheduled disclosure. Each Party shall have the
right to expeditiously review and recommend changes to any announcement
regarding this Agreement or the subject matter of this Agreement. Except as
otherwise required by law, the Party whose press release has been reviewed shall
remove any information the reviewing Party reasonably deems to be inappropriate
for disclosure.

     13.  Publication. Recipient shall have the right to publish the results of
          -----------
the work conducted by Recipient under this Agreement to the extent such results
do not contain Confidential Information of Company as described in Paragraph 3
and provided Company has the opportunity to review and comment on any proposed
manuscripts describing said work thirty (30) days prior to their submission for
publication. Recipient agrees to make any changes as per the Company's comments
prior to publication. If such submission would cause the loss of significant
foreign patent rights, Recipient will, at its option, either delete the enabling
portion of the proposed publication, or withhold publication for an additional
ninety (90) days until U.S. patent filings are completed.

Sequenom, Inc.                           Genzyme Corporation

By /s/ Hubert Koster                     By /s/ Evan M. Lebson
   ----------------------------             ---------------------------------

             __________________                       _______________________
Name (Print) Hubert Koster               Name (Print) Evan M. Lebson
             ------------------                       -----------------------
Title:  President and CEO                Title  Vice President - Treasurer
        -----------------------                 -----------------------------

Confidential                       Page 5
<PAGE>

Beta Test Agreement

                                  Schedule A


DNA MassArray(TM) Basic System Plus Evaluation Items include:

-    High-speed SpectroScan array mass spectrometer for
     separation, detection and characterization of the analyte molecules from a
     miniaturized array
-    SpectroJET dispenser for nanoliter sample transfer;
-    Automated Multipipettor;
-    BioMASS(TM) Workstation for data management and interpretation; and
-    Sequenom Magnetic Lifters.

The SEQUENOM 96 D SpectroChip(TM) will be made available     ***    during the
Beta test period for all tests that are performed for comparison of DNA
MassArray(TM) performance with other DNA analysis methods with result reported
to SEQUENOM on a confidential basis.



     *** Portions of this page have been omitted pursuant to a request for
Confidential Treatment and filed separately with the Commission.

Confidential                       Page 6