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                                                                         10.2.40

                              NEOPROBE CORPORATION
                         425 METRO PLACE NORTH SUITE 400
                             DUBLIN, OHIO 43017-1367

                                February 3, 1997

                            John L. Ridihalgh, Ph.D.
                                2112 Iuka Avenue
                               Columbus, OH 43201


Congratulations. You have been granted a Stock Option under Neoprobe's 1996
Stock Incentive Plan (the "Plan") on the following terms:

     1. NUMBER OF SHARES. The number of Shares of Common Stock of Neoprobe
     Corporation that you may purchase under this Option is: 27,000

     2. EXERCISE PRICE. The exercise price to purchase Shares under this Option
     is: $13-3/8 per Share.

     3. VESTING. One third (1/3) of the Shares originally subject to this Option
     will vest and become exercisable on each anniversary of the date of grant
     (February 3, 1997) if you have been an Employee of the Company continuously
     from the date of this Agreement shown above through the date when such
     portion of the Option.

     4. LAPSE. This Option will lapse and cease to be exercisable upon the
     earliest of:

          (i)   the expiration of 10 years from the date of this Agreement shown
                above,
          (ii)  9 months after you cease to be an Employee because of your death
                or disability,
          (iii) 90 days after your employment with Neoprobe or any Subsidiary is
                terminated by Neoprobe or such Subsidiary without cause, or
          (iv)  immediately upon termination of your employment with Neoprobe or
                any Subsidiary by Neoprobe or any Subsidiary for cause or by
                your resignation.

     5. TAXATION. This Option is a Nonqualified Option. You will have taxable
     income upon the exercise of this Option. At that time, you must pay to
     Neoprobe an amount equal to the required federal, state, and local tax
     withholding less any withholding otherwise made from your salary or bonus.
     You must satisfy any relevant withholding requirements before Neoprobe
     issues Shares to you.

     6. EXERCISE. This Option may be exercised by the delivery of this Agreement
     with the notice of exercise attached hereto properly completed and signed
     by you to the Treasurer of the Company, together with the aggregate
     Exercise Price for the number of Shares as to which the Option is being
     exercised, after the Option has become exercisable and before it has ceased
     to be exercisable. The Exercise Price must be paid in cash by (a) delivery
     of a certified or cashier's check payable to the order of Neoprobe in such
     amount, (b) wire transfer of immediately available funds to a bank account
     designated by Neoprobe, or (c) reduction of a debt of Neoprobe to you. This
     Option may be exercised as to less than all of the Shares purchasable
     hereunder, but not for a fractional share, nor may it be exercised as to
     less than one hundred (100) Shares unless it is exercised as to all of the
     Shares then available hereunder. If this Option is exercised as to less
     than all of the Shares purchasable hereunder, a new duly executed Option
     Agreement reflecting the decreased number of Shares exercisable under such
     Option, but otherwise of the same tenor, will be returned to you.

     7. NO TRANSFER. This Option may not be sold, pledged nor otherwise
     transferred other than by will or the laws of descent and distribution; and
     it may only be exercised during your lifetime by you. This Agreement is
     neither a negotiable instrument nor a security (as such term is defined in
     Article 8 of the Uniform Commercial Code).

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     8. NOT AN EMPLOYMENT AGREEMENT. This Agreement is not an employment
     agreement and nothing contained herein gives you any right to continue to
     be employed by or provide services to Neoprobe or affects the right of
     Neoprobe to terminate your employment or other relationship with you.

     9. PLAN CONTROLS. This Agreement is an Option Agreement (as such term is
     defined in the Plan) under Article 5 of the Plan. The terms of this
     Agreement are subject to, and controlled by, the terms of the Plan, as it
     is now in effect or may be amended from time to time hereafter, which are
     incorporated herein as if they were set forth in full. Any words or phrases
     defined in the Plan have the same meanings in this Agreement. Neoprobe will
     provide you with a copy of the Plan promptly upon your written or oral
     request made to its Vice President--Finance and Administration.

     10. MISCELLANEOUS. This Agreement sets forth the entire agreement of the
     parties with respect to the subject matter hereof and it supersedes and
     discharges all prior agreements (written or oral) and negotiations and all
     contemporaneous oral agreements concerning such subject matter. This
     Agreement may not be amended or terminated except by a writing signed by
     the party against whom any such amendment or termination is sought. If any
     one or more provisions of this Agreement shall be found to be illegal or
     unenforceable in any respect, the validity and enforceability of the
     remaining provisions hereof shall not in any way be affected or impaired
     thereby. This Agreement shall be governed by the laws of the State of
     Delaware.

Please acknowledge your acceptance of this Agreement by signing the enclosed
copy in the space provided below and returning it promptly to Neoprobe.


                                            NEOPROBE CORPORATION



                                            By: /s/ DAVID C. BUPP
                                                --------------------------------
                                                David C. Bupp
                                                President, COO

Accepted and Agreed to as of the date first set forth above:



/s/ JOHN L. RIDIHALGH
- ----------------------------
John L. Ridihalgh, Ph.D.



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                              OPTION EXERCISE FORM


The undersigned hereby exercises the right to purchase __________ shares of
Common Stock of Neoprobe Corporation pursuant to the Option Agreement dated
February 3, 1997 under the Neoprobe Corporation 1996 Stock Incentive Plan.


Date:
     -----------------------------

                                            --------------------------------
                                                 John L. Ridihalgh, Ph.D.


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Sign and complete this Option Exercise Form and deliver it to:

                              Neoprobe Corporation
                                 Attn: Treasurer
                              425 Metro Place North
                                    Suite 400
                             Dublin, Ohio 43017-1367

together with the option price in cash by (a) delivery of a certified or
cashier's check payable to the order of Neoprobe in such amount, (b) wire
transfer of immediately available funds to a bank account designated by
Neoprobe, or (c) reduction of a debt of Neoprobe to you.