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                                                                   Exhibit 10.15







                                        December 12, 1997





Bruce C. Horten, M.D.
IMPATH Inc.
1010 Third Avenue
New York, New York  10021

Dear Bruce:

                  In consideration of your service to IMPATH Inc. (the
"Company"), you and the Company agree as follows:

                  1. In connection with any merger or consolidation in which the
Company is not the surviving corporation and which results in the holders of the
outstanding  voting securities of the Company  (determined  immediately prior to
such merger or  consolidation)  owning  less than a majority of the  outstanding
voting securities of the surviving corporation (determined immediately following
such merger or consolidation),  or any sale or transfer by the Company of all or
substantially  all its assets or any tender  offer or exchange  offer for or the
acquisition, directly or indirectly, by any person or group of all or a majority
of the then outstanding voting securities of the Company,  all stock options for
the  purchase of common  stock of the Company  awarded to you prior to September
12, 1997  ("Options")  shall become  exercisable  in full,  notwithstanding  any
provision of the stock option plan of the Company  pursuant to which the Options
were granted or of the stock option  agreements or  certificates  evidencing the
Options,  on and after (i) the fifteenth day prior to the effective date of such
merger,  consolidation,  sale,  transfer  or  acquisition  or (ii)  the  date of
commencement  of such tender offer or exchange  offer,  as the case may be. With
respect to any Options which are incentive stock options,  the provisions of the
foregoing  sentence shall apply to the extent permitted by Section 422(d) of the
Code and such options in excess thereof shall,  immediately  upon the occurrence
of the event  described  in clause  (i) or (ii) of the  foregoing  sentence,  be
treated for all purposes as non-qualified stock options and shall be immediately
exercisable as such as provided in the foregoing sentence.
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                  2. In the event that your employment with the Company shall be
terminated by the Company without Cause (as hereinafter  defined),  and not as a
result of your death or Disability (as hereinafter  defined),  the Company shall
make a  severance  payment to you in an amount  equal to one year's  base salary
(determined at your highest  annualized rate of base salary in effect during the
one-year  period  ending  on the  date of  termination),  payable  in  bi-weekly
installments during the one-year period commencing on the date of termination of
your  employment.  You shall be under no obligation to seek other  employment or
otherwise to mitigate the Company's obligation to make such severance payment to
you;  provided,  however,  that if you do obtain another position (whether as an
employee,  consultant,  partner or otherwise)  during such one-year period,  the
Company  shall  have the right to offset  against  such  severance  payment  any
salary,  fees,  bonus or other cash  compensation  actually earned by you during
such one-year  period from such other position.  The Company shall,  during such
one-year period,  continue to provide you with health insurance  benefits on the
same basis,  including  Company-paid  premiums, as such benefits are provided to
employees of the Company. Your rights under the other benefit plans and programs
of the Company shall be  determined  in accordance  with the terms of such plans
and programs as then in effect.

                  For  purposes  of  this  agreement,   a  termination  of  your
employment  with the  Company by you for Good  Reason (as  hereinafter  defined)
shall constitute a termination of your employment by the Company without Cause.

                  For purposes of this  agreement:  "Cause"  shall mean (a) your
gross  neglect  or  willful  misconduct  in the  discharge  of your  duties  and
responsibilities to the Company,  (b) your material and repeated failure to obey
appropriate  directions from the Board of Directors of the Company which failure
has the effect of materially injuring the business or business  relationships of
the Company, (c) any act of willful  misappropriation by you against the Company
or (d) your  indictment,  conviction or plea of guilty or nolo  contendere  with
respect to a felony crime; "Good Reason" shall mean (a) a reduction in your base
salary from the  annualized  rate in effect on the date  hereof or as  hereafter
increased or (b) a demotion in your  position with the Company or change in your
duties and  responsibilities  inconsistent with your position,  which reduction,
demotion or change shall not have been  corrected by the Company within ten (10)
days following notice thereof by you to the Company; and "Disability" shall mean
your failure by reason of sickness, accident or physical or mental disability to
substantially perform the duties and
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responsibilities  of your  employment  with the  Company for a period of six (6)
months in any period of twelve (12) consecutive months.

                  3. You agree that, in  consideration  of your  employment with
the Company, you will not, during the period of your employment with the Company
and  thereafter  for a  period  of  one  (1)  year  commencing  on the  date  of
termination  of your  employment  with the  Company,  (a)  engage,  directly  or
indirectly,   whether  as   principal,   agent,   distributor,   representative,
consultant,  employee, partner,  stockholder,  limited partner or other investor
(other than an investment of not more than (i) five percent (5%) of the stock or
equity of any  corporation the capital stock of which is publicly traded or (ii)
five percent (5%) of the ownership interest of any limited  partnership or other
entity) or  otherwise,  in any business in  competition  with the business  then
conducted by the Company or any of the Company's  subsidiaries  (the Company and
the Company's  subsidiaries,  being hereinafter  collectively referred to as the
"Company Group"), or (b) solicit or entice or endeavor to solicit or entice away
from any  member of the  Company  Group any person  who was an  employee  of any
member of the Company Group,  either for your own account or for any individual,
firm or  corporation,  or employ,  directly  or  indirectly,  any person who was
during  the one (1)  year  period  ending  on the  date of  termination  of your
employment an employee of any member of the Company Group.

                  4. In the event of a breach or threatened breach by you of any
of the provisions of Section 3 of this  agreement,  you hereby consent and agree
that the  Company  shall  (i) be  entitled  to cease  payment  of the  severance
referred to in Section 2 of this agreement and (ii) be entitled to an injunction
or similar equitable relief from any court of competent jurisdiction restraining
you from  committing  or  continuing  any such  breach or  threatened  breach or
granting  specific  performance of any act required to be performed by you under
any of such  provisions,  without the  necessity of showing any actual damage or
that money damages would not afford an adequate remedy and without the necessity
of posting any bond or other  security.  Nothing  herein  shall be  construed as
prohibiting  the Company from  pursuing  any other  remedies at law or in equity
which it may have with respect to any such breach or threatened breach.

                  5. This agreement  shall be deemed a contract made under,  and
for all purposes shall be construed in accordance with, the laws of the State of
New York applicable to contracts to be performed entirely within such State.
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                  6.  This  agreement   contains  all  the   understandings  and
representations  between the parties  hereto  pertaining  to the subject  matter
hereof.

                  7. No provision of this  agreement  may be amended or modified
unless such amendment or  modification is agreed to in writing and signed by you
and by a duly authorized representative of the Company.

                  8. Should any  provision of this  agreement be held by a court
or  arbitration  panel  of  competent  jurisdiction  to be  enforceable  only if
modified,  such holding  shall not affect the validity of the  remainder of this
agreement,  the balance of which shall  continue to be binding  upon the parties
hereto with any such  modification to become a part hereof and treated as though
originally set forth in this agreement.  The parties further agree that any such
court  or  arbitration  panel  is  expressly   authorized  to  modify  any  such
unenforceable provision of this agreement in lieu of severing such unenforceable
provision  from  this  agreement  in its  entirety,  whether  by  rewriting  the
offending  provision,  deleting any or all of the  offending  provision,  adding
additional language to this agreement,  or by making such other modifications as
it deems  warranted  to carry out the intent  and  agreement  of the  parties as
embodied  herein to the maximum extent  permitted by law. The parties  expressly
agree that this agreement as so modified by the court or arbitration panel shall
be binding upon and enforceable  against each of them. In any event,  should one
or more of the  provisions of this  agreement be held to be invalid,  illegal or
unenforceable in any respect,  such invalidity,  illegality or  unenforceability
shall  not  affect  any  other  provisions  hereof,  and if  such  provision  or
provisions are not modified as provided above, this agreement shall be construed
as if such invalid, illegal or unenforceable provisions had never been set forth
herein.

                  9.  Anything to the  contrary  notwithstanding,  all  payments
required to be made by the Company  hereunder shall be subject to withholding of
such amounts relating to taxes as the Company may reasonably determine it should
withhold pursuant to any applicable law or regulation.


                       *          *          *
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                  Please  indicate your  acceptance  of and  agreement  with the
foregoing by signing and returning this agreement to the Company, whereupon this
shall constitute a binding agreement between you and the Company.


                                            Very truly yours,

                                            IMPATH INC.



                                            By    /s/ Anu D. Saad
                                              -----------------------

Accepted and Agreed:



   /s/ Bruce C. Horten
---------------------------
       Bruce C. Horten