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                                                                    EXHIBIT 10.1


                            STOCK PURCHASE AGREEMENT


     AGREEMENT, made as of May 18, 2006, between Israel M. Stein (the "Seller")
and Third Security Staff 2001 LLC (the "Buyer").

     WHEREAS, the Seller is willing to sell to the Buyer, and the Buyer is
willing to purchase from the Seller, One Hundred Thousand (100,000) shares of
Common Stock (the "Shares") of Clinical Data, Inc., a Delaware corporation (the
"Company"), currently held by the Seller.

     ACCORDINGLY, THE PARTIES AGREE AS FOLLOWS:

     1. Sale of Shares. The Seller hereby agrees to sell to the Buyer, and the
Buyer hereby agrees to purchase from the Seller, all of the Shares. The Buyer
hereby acknowledges that the Shares do not represent the entire equity interest
of the Seller in the Company and agrees that the transactions contemplated by
this Agreement will not create in, or transfer to, the Buyer any right or
interest in any other security of the Company held by the Seller.

     2. Purchase Price. The purchase price for the Shares is Two Million Dollars
($2,000,000) (the "Purchase Price"). The Purchase Price shall be paid in the
form of a $2,000,000 promissory note of even date from the Buyer to the Seller
in the form attached hereto as Exhibit A (the "Promissory Note"), against
delivery by the Seller to the Buyer of a certificate or certificates
representing the Shares registered in the name of the Buyer or, if not so
registered, accompanied by stock powers in form sufficient to permit transfer of
the Shares into the name of the Buyer on the books of the stock transfer agent
of the Company.

     3. Representations and Warranties of the Seller. The Seller represents and
warrants to the Buyer as follows:

          (a) Shares. The Seller is the lawful owner of the Shares, and the
     Seller has the full power and authority to sell the Shares, free and clear
     of any liens or encumbrances whatsoever. All of the Shares have been, to
     the best knowledge of the Seller, validly issued and are fully paid and
     nonassessable; and no person has any present or future right (conditional,
     preemptive or otherwise) to acquire any of the Shares. Upon delivery of
     such Shares and payment therefor pursuant hereto, good and valid title to
     all such Shares free and clear of all liens or encumbrances whatsoever,
     options, warrants, purchase rights, contracts, commitments, equities,
     claims and demands will be transferred to Buyer, and such Shares shall be
     validly issued, fully paid and nonassessable.

          (b) No Breach or Conflict. The sale of the Shares contemplated by this
     Agreement does not conflict with, or result in a breach of, or a default
     under, or give rise to a right of acceleration under, any agreement or
     instrument to which the Seller is a party.

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          (c) Consent. No consent of any other person, and no notice to, filing
     or registration with, or consent, approval or authorization of, any court
     or governmental authority, regulatory or self-regulatory agency or any
     other third party is necessary or is required to be made or obtained by
     Seller, in connection with the execution and delivery of this Agreement or
     the consummation of the transactions contemplated hereby, except as may be
     required under the Blue Sky laws of the jurisdiction in which the Buyer is
     resident.

          (d) Litigation. There is no litigation, arbitration proceeding,
     governmental investigation, citation or action of any kind pending or, to
     the knowledge of Seller, proposed or threatened that seeks restraint,
     prohibition, damages or other relief in connection with this Agreement or
     the consummation of the transactions contemplated hereby.

          (e) Fees and Expenses of Brokers and Others. Seller is not committed
     to any liability for any brokers' or finders' fees or any similar fees in
     connection with the transactions contemplated hereby, and Seller has not
     retained any broker or other intermediary to act on its behalf in
     connection with the transactions contemplated by this Agreement.

          (f) Purchase for Investment. Seller is acquiring the Promissory Note
     solely for Seller's own account for investment and not with a view to or
     for sale in connection with any distribution thereof. Seller acknowledges
     that the Promissory Note has not been registered under the Securities Act
     of 1933, as amended (the "Securities Act"), the Promissory Note currently
     is not freely tradable because it constitutes restricted securities and
     Seller must continue to bear the economic risk of the investment in the
     Promissory Note unless the Promissory Note is subsequently registered under
     the Securities Act and applicable state securities laws or an exemption
     from such registration is available.

          (g) Truth and Completeness of Representations and Warranties. None of
     the information contained in the representations and warranties of the
     Seller set forth in this Agreement contains any untrue statement of a
     material fact or omits or will omit to state a material fact necessary to
     make the statements contained herein or therein not misleading.

     4. Representations and Warranties of the Buyer. The Buyer represents and
warrants to the Seller as follows:

          (a) Organization of Buyer. Buyer is a limited liability company duly
     formed and validly existing under the laws of the Commonwealth of Virginia.

          (b) Investment Intent. The Buyer is acquiring the Shares for its own
     account for investment, not for the interest of any other person, not for
     resale to any other person and not with a view to or in connection with a
     sale or distribution, as such term is defined in the Securities Act.


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          (c) Knowledge and Experience. The Buyer is an "accredited investor"
     (as such term is defined in Regulation D under the Securities Act), is
     knowledgeable and experienced in businesses of the sort conducted by the
     Company.

          (d) Investment Risk. The Buyer understands that the Shares were
     acquired by the Seller in a transaction exempt from the registration
     requirements of the Securities Act, and are being sold and transferred to
     the Buyer in a transaction which the Seller (in reliance on the
     representations and warranties made by the Buyer herein) believes exempt
     from such registration requirements; and that the Buyer may be required to
     hold the Shares indefinitely. The Buyer is capable of evaluating the merits
     and risks involved in the acquisition of the Shares and is capable of
     bearing the economic risk of such investment.

          (e) Resale. The Buyer is aware that any resale inconsistent with the
     Securities Act may create liability on its part and/or the part of the
     Seller, and agrees not to assign, sell, pledge, transfer or otherwise
     dispose of or transfer any of the Shares unless registered under the
     Securities Act and applicable state securities laws or an exemption from
     such registration is available.

          (f) Legend. The certificate representing the Shares will contain a
     legend substantially as follows:

               "The shares represented hereby have not been registered under the
               Securities Act of 1933 (the "Act"), or any state securities or
               blue sky laws and may not be offered, sold, transferred,
               hypothecated or otherwise assigned except pursuant to a
               registration statement with respect to such shares which is
               effective under the Act or pursuant to an available exemption
               from registration under the Act relating to the disposition of
               securities and in accordance with applicable state securities and
               blue sky laws."

          (g) Liquidity. Buyer has no need for liquidity in this investment.

          (h) No Prospectus. The Buyer is acquiring the Shares without being
     furnished any offering literature or prospectus by the Seller.

          (i) Risk Factors. The undersigned understands that an investment in
     the Shares involves significant risks, and the undersigned has carefully
     reviewed and is aware of all of the risk factors related to the purchase of
     the Shares.

     5. Guaranty. The parties hereto agree that it is a condition precedent to
delivery and acceptance of the Promissory Note that Randal J. Kirk shall have
executed and delivered to the Seller a Guaranty in the form attached hereto as
Exhibit B.

     6. Indemnification.

          (a) Seller's Indemnification. Seller hereby indemnifies and holds
     Buyer and its directors, officers, members and affiliates (collectively,
     the " Buyer Indemnified


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     Parties") harmless from and against, and agrees to defend promptly the
     Buyer Indemnified Parties from and reimburse the Buyer Indemnified Parties
     for, any and all losses, liabilities, claims, damages (including incidental
     and consequential damages), costs, expenses (including costs of
     investigation and defense and reasonable attorneys' fees) and obligations
     (hereinafter referred to collectively as "Losses") that the Indemnified
     Parties may at any time suffer or incur, or become subject to, as a result
     of or in connection with: (i) any material breach or inaccuracy of any of
     the representations and warranties made by Seller in this Agreement or any
     other agreement or instrument delivered by Seller pursuant to this
     Agreement; and (ii) any failure of Seller to carry out, perform, satisfy
     and discharge any of its covenants, agreements, undertakings, liabilities
     or obligations under this Agreement or under any of the agreements and
     instruments delivered by Seller pursuant to this Agreement.

          (b) Buyer's Indemnification. Buyer hereby indemnifies and holds Seller
     harmless from and against, and agrees to defend promptly the Seller from
     and reimburse the Seller for, any and all Losses that Seller may at any
     time suffer or incur, or become subject to, as a result of or in connection
     with: (i) any material breach or inaccuracy of any of the representations
     and warranties made by Buyer in this Agreement, the Promissory Note or any
     other agreement or instrument delivered by Buyer pursuant to this
     Agreement; and (ii) any failure of Buyer to carry out, perform, satisfy and
     discharge any of its covenants, agreements, undertakings, liabilities or
     obligations under this Agreement, the Promissory Note or under any of the
     agreements and instruments delivered by Buyer pursuant to this Agreement.

     7. Successors and Assigns. This Agreement shall be binding upon and shall
inure to the benefit of the undersigned parties and their respective heirs,
personal representatives, successors and assigns.

     8. Entire Agreement and Amendments. This Agreement represents the entire
agreement of the parties with respect to the subject matter hereof, and no other
agreement with respect thereto, including any prior written or oral
representation or understanding of the parties, shall have any further force or
effect. The Buyer and the Seller each represents and warrants to the other that,
in entering this Agreement, he has relied on no statements, representations,
inducements or promises made by the other party except as are expressly set
forth in this Agreement. This Agreement may be modified only by a subsequent
writing signed by both parties to this Agreement.

     9. Governing Law. This Agreement shall be governed by, and construed in
accordance with, the laws of the State of Delaware.


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     IN WITNESS WHEREOF, the parties have duly executed this Agreement as of the
day and year first above written.


                                              THE BUYER:

                                              THIRD SECURITY STAFF 2001 LLC



                                              /s/Randal J. Kirk
                                              ----------------------------------
                                              By: Randal J. Kirk
                                              Title: Manager


                                              THE SELLER:


                                              /s/Israel M. Stein
                                              ----------------------------------
                                              Israel M. Stein


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