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                                                                Exhibit 10.13


November 21, 1999

Stephan S. Monroe, Ph.D.
Viral Gastroenteritis Section
Division of Viral and Rickettsial Diseases
MailStop G04
Centers for Disease Control and Prevention
1600 Clifton Rd., NE
Atlanta, Georgia 30333

Dear Dr. Monroe,

This letter is to confirm the understanding between Life Sciences, Inc. and the
Gastroenteritis Section of the Centers for Disease Control with respect to the
impending initiation of work on a NASBA-based test for detection of Norwalk-like
viruses prior to the execution of a definitive cooperative research and
development agreement (CRADA) between the parties.

As we discussed in our meeting on November 17, 1999, completion of the work
within a timeframe consistent with the mission of the Centers can be achieved
only if there are no significant delays in the start-up and pursuit of the
effort. At the same time, the dollar value and missed business opportunity
implications of Life Sciences' in-kind contributions to the early stages of the
effort are of sufficient magnitude to warrant the assurances requested by LSI in
this communication. In addition, because LSI's work on this effort must begin in
earnest on November 29, 1999 to meet the timing discussed, the prompt execution
of this letter approaches the imperative.

Further with respect to our November 17 discussions, Life Sciences represented
that it will provide with respect to the CRADA, at no cost to the Centers, the
items set out below as its base contribution to the effort described above:

                  (i)* The financial wherewithal to support a post-doctoral
         level scientist posted at the Centers, or at a location designated by
         the Centers, to work on this effort for the initial 12 months of the
         proposed CRADA. Funding at the same or adjusted level will be provided
         for a second 12-month period if the program objectives of the initial
         12 months are achieved. (This element of direct financial support,
         including employee benefit related overhead, is not expected to exceed
         $60,000 on an annual basis);

                  (ii) The transfer of a significant body of knowledge to CDC
         based scientists in the performance of nucleic acid sequence based
         amplification (NASBA); the design of primers necessary for
         amplification of RNA and DNA templates using NASBA; and the detection
         and analysis of the amplicons arising from these reactions using a
         proprietary technology.




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Stephan S. Monroe, Ph.D.             November 21, 1999                   Page 2

                  (iii) A quantity of NASBA amplification and detection reagents
         (enzyme, primers, probe-labeled liposomes, etc.) and supplies
         sufficient to support this effort as ultimately defined in the scope of
         work of the proposed CRADA for the full term of the agreement;

                  (iv) A quantity (not to exceed 20 ) of specially modified,
         hand-held densitometers for low-cost, high-throughput qualitative and
         semi-quantitative assessment of NASBA reactions using a lateral flow
         cassette and a proprietary technology;

                  (v)* A quantity (not to exceed 3) of the LSI electrochemical
         NASBA analyzers for low-cost, high-throughput quantitative assessment
         of NASBA reactions using a proprietary technology;

                  (vi)* The use of an Organon Teknika automated nucleic acid
         extractor apparatus for the full term of the CRADA;

                  (vii)* The use of an Organon Teknika electrochemiluminescece
         detector for not less than the initial 6 months of the work effort;
         and.

                  (viii)* The assembly and support of a LSI-
         multiple-academic-center consortium to support the development of
         technology and methods for recovery of Norwalk-like virus/RNA templates
         in low copy number from non-patient related matrices to include water
         and food.

         *   To be provided only upon execution of the definitive CRADA.

While the language of the draft agreement provided to us contemplates that, at
the successful completion of the work effort to be described in the CRADA,
certain U.S. government-owned intellectual property will be licensed to LSI for
a range of applications, excluding vaccine development and production, it is our
expectation that certain additional assurances can be provided by your Section
in order to secure LSI's contributions during the period prior to the execution
of a definitive CRADA. Specifically, the Gastroenteritis Section agrees by
execution of this letter that during the period prior to execution of the
definitive agreement, and provided Life Sciences faithfully provides those
elements of the resources described above that are designated as appropriate to
the work to be carried out during the pre-agreement period, the Gastroenteritis
Section will collaborate exclusively with Life Sciences on development of the
NASBA-based test for Norwalk-like viruses contemplated in our discussions.

It is our current plan to begin synthesis of the required primers and probes for
amplification of certain of the Norwalk-like viruses and detection of both the
Astro and Norwalk-like viruses during this coming Thanksgiving week. This
timetable is necessitated by the absolute requirement that work on production of
the labeled liposomes be carried out at Cornell University beginning on November
29 as an element of the transfer of a licensed technology. If this schedule is
not met, it is doubtful that the detection components will be available to us




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Roger I. Glass M.D., Ph.D.           November 21, 1999                    Page 3

before mid January 2000. I sincerely hope that timely execution of this letter
of intent will permit us to adhere to this plan.

Please sign where indicated below, and return to me via facsimile at
727-347-2957. Please call me at 727 345.9371 or 727 420.1795 if you have any
questions. I look forward to the continuation of the current pace of the
proposed activity.

Sincerely,

LIFE SCIENCES, INC.

/s/ Alex A. Burns
-----------------------------
Alex A. Burns, Vice President
                                     ACCEPTED AND AGREED:
                                     Viral Gastroenteritis Section
                                     Centers for Disease Control and Prevention

                                     /s/ Stephan S. Monroe
                                     ------------------------------------------
                                         Stephan S. Monroe


/i/ SSM
This letter is an accurate summary of outline of a CRADA discussed at a meeting
on 17 November 1999 between Mr. Alex Burns, Life Sciences, Inc., and Drs. Roger
Glass and Stephan Monroe, CDC