Common Stock

                                                                       EXHIBIT 1

                         MediChem Life Sciences, Inc.
                         ----------------------------


                                 Common Stock

                               ($0.01 Par Value)
                                                              September 27, 2000

UBS Warburg LLC
Chase Securities, Inc.
Xxxxxxx Xxxxx & Company L.L.C.
As Representatives of the several Underwriters

c/o UBS Warburg LLC
    000 Xxxx Xxxxxx
    Xxx Xxxx, Xxx Xxxx 00000

Ladies and Gentlemen:

      This letter is being delivered to you in connection with the proposed
Underwriting Agreement (the "Underwriting Agreement") to be entered into by and
among MediChem Life Sciences, Inc., a Delaware corporation (the "Company"), and
you, as representatives of the several underwriters, with respect to the initial
public offering ("Initial Public Offering") of Common Stock, $0.01 par value per
share (the "Common Stock"), of the Company.

      In order to induce you to enter into the Underwriting Agreement, the
undersigned will not, without the prior written consent of UBS Warburg LLC, (i)
sell, offer to sell, contract to sell, hypothecate, pledge, grant any option to
sell or otherwise dispose of, or file (or participate in the filing of) a
registration statement with the Securities and Exchange Commission (the
"Commission") in respect of, or establish or increase a put equivalent position
or liquidate or decrease a call equivalent position within the meaning of
Section 16 of the Securities Exchange Act of 1934, as amended, and the rules and
regulations of the Commission promulgated thereunder with respect to, any shares
of Common Stock or any securities convertible into or exercisable or
exchangeable for Common Stock, (ii) enter into any swap or other arrangement
that transfers to another, in whole or in part, any of the economic consequences
of ownership of Common Stock or any securities convertible into or exercisable
or exchangeable for Common Stock, whether any such transaction is to be settled
by delivery of Common Stock or such other securities, in cash or otherwise, or
(iii) publicly announce an intention to effect any transaction specified in
clause (i) or (ii), in the case of each of clauses (i), (ii) and (iii) for a
period of 180 days after the date of the final prospectus in connection with the
Initial Public Offering. The foregoing notwithstanding, the undersigned may
dispose of shares of Common Stock which are disposed of as bona fide gifts
approved by UBS Warburg LLC to transferees entering into lock-up agreements with
you to the effect stated above.

      If for any reason the Underwriting Agreement shall be terminated prior to
the time of purchase (as defined in the Underwriting Agreement), the agreement
set forth above shall likewise be terminated.


                                                Yours very truly,


                                                By:
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