Document:

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                                                                    Exhibit 10.8
                                                                    ------------

         TAX RESPONSIBILITY ALLOCATION AGREEMENT (the "Agreement"), dated as of
_____ between Merck & Co., Inc., a New Jersey Corporation ("Distributing"), and
MedcoHealth Solutions, Inc., a Delaware corporation ("Controlled" and together
with Distributing, the "Companies").

         WHEREAS, Distributing owned 100% of the membership interests in Merck
Medco Care LLC, a Delaware limited liability company ("Medco") and, as part of a
plan intended to culminate in the Distribution (as defined below), has caused
Medco to convert under Delaware law to a corporation which has adopted the name
of Controlled;

         WHEREAS, pursuant to such plan and as part of a series of transactions
resulting in a public offering of not more than 19.9% of Controlled's shares,
Distributing will exchange not more than 19.9% of its stock in Controlled for
outstanding Distributing commercial paper (the "Exchange") on the date of the
Exchange (the "Exchange Date");

         WHEREAS, pursuant to such plan, the board of directors of Distributing
has determined it would be in the best interests of Distributing and its
shareholders to distribute, after the Exchange (the "Distribution"), all of
Distributing's remaining shares in Controlled to the Distributing shareholders
on the terms and conditions set forth in the Master Separation and Distribution
Agreement dated the date hereof between Distributing and Controlled (the
"Distribution Agreement") (the date of such Distribution, the "Distribution
Date");

         WHEREAS, the Companies intend that the Distribution qualify as a
tax-free spin-off pursuant to Section 355 and as a reorganization pursuant to
Section 368(a)(1)(D) of the Internal Revenue Code of 1986, as amended (the
"Code");

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         WHEREAS, as of the date hereof, Distributing is the common parent of an
affiliated group of domestic corporations, including Controlled, which has
elected to file consolidated federal income tax returns (the "Distributing
Consolidated Group") and, as a result of the Distribution, Controlled will not
be a member of the Distributing Consolidated Group for the portion of the
taxable year following the Distribution or in future taxable years;

         WHEREAS, the Companies desire (i) to allocate the responsibilities for
Income Tax (as hereinafter defined) of Controlled, (ii) to allocate the
responsibilities for Other Controlled Tax (as hereinafter defined) and (iii) to
provide for certain additional Tax (as hereinafter defined) matters;

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein, the Companies (each on behalf of itself, each of its
subsidiaries as of the Distribution Date, and its future subsidiaries) hereby
agree as follows:

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                                    ARTICLE I

                                   DEFINITIONS

         The following terms shall have the following meanings (such meanings to
apply equally to both the singular and the plural forms of the terms defined).
All section references are to this Agreement unless otherwise stated.

         "Affiliate" means any entity that directly or indirectly is Controlled
          ---------
by the person or entity in question.

         "Control" means the possession, directly or indirectly, of the power to
          -------
direct or cause the direction of the management and policies of a person,
whether through ownership of voting securities, by contract or otherwise.

         "Controlled Business" means any businesses formerly carried out by
          -------------------
Distributing (directly or indirectly), that are now carried out by the
Controlled Group and any assets owned directly or indirectly by Distributing
that are now owned by the Controlled Group.

         "Controlled Group" shall mean, collectively or separately, Controlled
          ----------------
and any Affiliate of Controlled for which Controlled has any direct or indirect
Tax liability.

         "Controlled Separate Federal Income Tax Liability" means, with respect
          ------------------------------------------------
to any period for which the Controlled Group is included in Distributing's
Consolidated Group, the liability for U.S. federal income tax (including
"alternative minimum tax", if any) of the Controlled Group computed as though
the Controlled Group filed a U.S. federal income tax return separate from
Distributing for such taxable period, which amount shall not be less than zero.

         "Controlled Separate State Tax Liability" means, with respect to any
          ---------------------------------------
period for which the Controlled Group is included in any of Distributing's
combined or unitary

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groups, the liability for state or local Income Tax of the Controlled Group
computed as though the Controlled Group filed a Tax Return separate from
Distributing for such taxable period, which amount shall not be less than zero.

         "Distributing Group" shall mean, collectively or separately,
          ------------------
Distributing and any Affiliate of Distributing for which Distributing has any
direct or indirect Tax liability, other than any member of the Controlled Group.

         "Distributing Subsidiary" shall mean an Affiliate of Distributing other
          -----------------------
than Controlled or any Affiliate of Controlled.

         "Income Tax" means any federal, state or local tax imposed on net
          ----------
income including the Michigan Single Business Tax, but not including Washington
State's "business and occupation tax" or any municipal gross receipts tax
("patente") imposed in Puerto Rico.

         "IRS Private Letter Ruling" means any private letter ruling from the
          -------------------------
United States Internal Revenue Service issued in connection with the
Distribution.

         "Other Controlled Tax" means any Tax of the Controlled Group or with
          --------------------
respect to the Controlled Business that is not an Income Tax (whether payable
directly by Controlled Group or payable by a combined or unitary group that
includes the Controlled Group to the extent of Controlled Group's portion of
such Tax).

         "Post-Distribution Period" means all taxable periods or portions of
          ------------------------
periods beginning on or after the Distribution Date.

         "Post-Exchange Period" means all taxable periods or portions of periods
          --------------------
beginning on or after the Exchange Date and which is not a Post-Distribution
Period.

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         "Pre-Exchange Period" means all taxable periods or portions of periods
          -------------------
ending before the Exchange Date.

         "Tax" means any income, gross income, gross receipts, profits, capital
          ---
stock, franchise, withholding, payroll, social security, workers compensation,
unemployment, disability, property, ad valorem, stamp, excise, severance,
occupation, service, sales, use, license, lease, transfer, import, export, value
added, alternative minimum, estimated or other similar tax (including any fee,
assessment, or other charge in the nature of or in lieu of any tax) imposed by
any governmental entity or political subdivision thereof, and any interest,
penalties, additions to tax, or additional amounts in respect of the foregoing
imposed on any taxpayer or consolidated, combined or unitary group of taxpayers.

         "Tax Authority" means, with respect to any Tax, the governmental entity
          -------------
or political subdivision thereof that imposes such Tax, and the agency (if any)
charged with the collection of such Tax for such entity or subdivision.

         "Tax Benefit" means the amount that any item of loss, deduction or
          -----------
credit (or any other item) decreases Taxes paid or payable including any
interest with respect thereto or interest that would have been payable but for
such item, net of any Tax imposed on such interest.

         "Tax Contest" means an audit, review, examination, or any other
          -----------
administrative or judicial proceeding with the purpose or effect of
redetermining any Tax (including any administrative or judicial review of any
claim for refund).

         "Tax Detriment" means the amount that any item of income or gain (or
          -------------
any other item) increases Taxes paid or payable including any interest with
respect thereto.

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         "Tax Return" means any report of Tax due, any claims for refund of Tax
          ----------
paid, any information return with respect to Tax, any election made with respect
to Tax, or any other similar report, statement, declaration, or document
required to be filed under the Code or other law in respect of Tax, including
any attachments, exhibits, or other materials submitted with any of the
foregoing, and including any amendments or supplements to any of the foregoing
for any taxpayer or consolidated, combined or unitary group of taxpayers.

                                   ARTICLE II

                             RESPONSIBILITY FOR TAX

        2.01      Responsibility for Tax.
                  ----------------------

                  (a) Distributing shall be responsible for and indemnify and
hold harmless the Controlled Group from (i) any liability for Income Tax of the
Controlled Group with respect to the Pre-Exchange Period; (ii) any Income Tax of
the Distributing Group by reason of Controlled Group being severally liable for
such Income Tax pursuant to Treasury Regulations Section 1.1502-6 or any
analogous provision of state or local law; and (iii) any item described in
Section 3.01(a) to the extent not covered by Section 3.01(b).

                  (b) For all Post-Exchange Periods in which Controlled is a
member of the Distributing Consolidated Group, Controlled shall be responsible
for and shall timely pay to Distributing (at the time specified in Section
2.04), an amount equal to the Controlled Separate Federal Income Tax Liability,
as calculated by Distributing in good faith and in the normal course of
business.

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                  (c) For all Post-Exchange Periods in which Controlled or any
other member of the Controlled Group is a member of a state or local
consolidated, combined or unitary group of which any member of the Distributing
Group is the parent, Controlled shall be responsible for and shall timely pay
Distributing (at the time specified in Section 2.04), an amount equal to the
Controlled Separate State Tax Liability, as calculated by Distributing in good
faith and in the normal course of business.

                  (d) Controlled shall be responsible for, and indemnify and
hold harmless the Distributing Group from (i) all Income Tax of the Controlled
Group with respect to a Post-Exchange Period not covered by 2.01(b) and (c)
above, (ii) all Income Tax of the Controlled Group with respect to a
Post-Distribution Period, (iii) all Other Controlled Tax (regardless of which
period it relates to) and (iv) any act for which Controlled is liable under
Section 3.01(b).

                  (e) Distributing shall be responsible for and shall pay
Controlled the amount of any reduction in Income Tax in a Post-Exchange Period
when and if actually realized by the Distributing Group which is attributable to
the utilization of a "net operating loss" generated by the Controlled Group
(calculated as if the Controlled Group were a separate taxpayer).

                  (f) For purposes of this Agreement, in the case of any taxable
period that begins before and ends after the date of the Exchange or begins
before and ends after the Distribution Date, the amount of all Income Tax
payable for a portion of a period shall be the amount which would have been
payable if that portion of a period constituted a separate taxable period
beginning on the date such portion of a period began and ending

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on the date such portion of a period ended, or in such other manner as the
parties may agree.

         2.02     Refunds and Tax Benefits.
                  ------------------------

                  (a) Refunds and Carrybacks. (i) Except as provided in (vi)
below, Distributing shall be entitled to any refunds of Income Tax paid by or on
behalf of the Controlled Group (including refunds paid by means of a credit
against other or future Tax liabilities) arising with respect to taxable periods
ending on or before the Exchange Date.

                  (ii) Controlled shall be entitled to any refunds of Income Tax
paid by or on behalf of the Controlled Group (including refunds paid by means of
a credit against other or future Tax liabilities) arising with respect to
taxable periods beginning on or after the Exchange Date.

                  (iii) Distributing and Controlled agree to allocate refunds of
Income Tax of the Controlled Group (including refunds paid by means of a credit
against other or future Tax liabilities) arising with respect to taxable periods
that begin before and end after the Exchange Date to whichever of Distributing,
Controlled, or both initially bore the items to which such refund is
attributable.

                  (iv) Controlled shall be entitled to any refunds or credits of
Other Controlled Tax (including refunds paid by means of a credit against other
or future Tax liabilities).

                  (v) Controlled shall promptly forward to Distributing or
reimburse Distributing for any refunds due Distributing (pursuant to the terms
of this Section 2.02(a)) after receipt thereof (less any net Tax Detriment
imposed with respect to

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such refunds or any interest paid with respect to such refunds), and
Distributing shall promptly forward to Controlled or reimburse Controlled for
any refunds due Controlled (pursuant to the terms of this Section 2.02(a)) after
receipt thereof (less any net Tax Detriment imposed with respect to such refunds
or any interest paid with respect to such refunds). In the case of a refund
received in the form of a credit against other or future Tax liabilities,
reimbursement in respect of such refund shall be due in each case on the due
date for payment of the Tax against which such refund has been credited. If
Distributing reasonably so requests, Controlled, at Distributing's expense,
shall file for and pursue any refund to which Distributing is entitled under
this Section 2.02(a). If Controlled reasonably so requests, Distributing, at
Controlled's expense, shall file for and pursue any refund to which Controlled
is entitled to under this Section 2.02(a).

                  (vi) Distributing agrees that if the Controlled Group carries
back any item of loss, deduction or credit which arises in any taxable period
ending after the Distribution Date into any taxable period beginning before the
Distribution Date, then Controlled shall be entitled to any Tax Benefit or
refund of Tax realized as a result of the carryback.

                  (b) Allocation of Benefits. If any adjustments shall be made
to any Tax Returns relating to Income Taxes of the Controlled Group or the
Distributing Group for the Pre-Exchange Period as a result of or in settlement
of any Tax Contest, and if such adjustment results in any Tax Detriment to
Distributing or any Affiliate of Distributing (including the Controlled Group)
with respect to such period and any Tax Benefit to the Controlled Group for any
taxable period (or portion thereof) beginning after the Exchange Date,
Controlled shall pay to Distributing the amount of such Tax Benefit at such time
or

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times as and to the extent that the Controlled Group realizes such benefit
through a refund of Tax or reduction in the amount of Tax which the Controlled
Group would otherwise have had to pay if such adjustment had not been made.

                  If any adjustments shall be made to any Tax Returns relating
to Income Taxes of the Controlled Group for any Post-Exchange Period or
Post-Distribution Period as a result of or in settlement of any Tax Contest, and
if such adjustment results in any Tax Detriment to the Controlled Group with
respect to such period and any Tax Benefit to Distributing or any Affiliate of
Distributing (including the Controlled Group) for the Pre-Exchange Period,
Distributing shall pay to Controlled the amount of such Tax Benefit at such time
or times as and to the extent that Distributing or any Affiliate of Distributing
realizes such benefit through a refund of Tax or reduction in the amount of Tax
which Distributing or such Affiliate of Distributing would otherwise have had to
pay if such adjustment had not been made.

         2.03     Option Deductions.
                  -----------------

                  (a) Acquired Company Options.

                  (i) Upon the exercise of any Acquired Company Option (as
defined in (d) below) following the Distribution, (1) Controlled shall claim any
Tax deduction attributable to such exercise on its Tax Return and Distributing
shall not claim such deduction on its Tax Return as originally filed, (2)
Controlled shall pay to Distributing an amount equal to the Option Tax Value (as
defined in (d) below), and (3) to the extent that such deduction is disallowed
to Controlled, and a Tax Authority determines (a "Determination") that
Distributing is entitled to such deduction to any extent, Distributing shall, to
such extent, repay to Controlled the portion of the Option

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Tax Value attributable to such Acquired Company Option.

                  (ii) Controlled shall pay to Distributing the Option Tax Value
under this Section 2.03(a) within 30 days of the date that Distributing notifies
Controlled of the amount thereof. Distributing shall pay to Controlled the
Option Tax Value under this Section 2.03(a) within 30 days of the date that
Controlled notifies Distributing of the receipt of a Determination (which
notification shall be made promptly after receipt thereof).

                  (b) Merck Options. Upon the exercise of any Merck Option (as
defined in (d) below) following the Distribution, (i) Distributing shall claim
any Tax deduction attributable to such exercise on its Tax Return and Controlled
shall not claim such deduction on its Tax Return as originally filed, and (ii)
to the extent such deduction is disallowed to Distributing, and a Tax Authority
makes a Determination that Controlled is entitled to such deduction, Controlled
shall, to such extent, pay to Distributing, within 30 days of the date that
Distributing notifies Controlled of the receipt of such Determination (which
notification shall be made promptly after receipt thereof), the Option Tax Value
attributable to such Merck Option.

                  (c) All Other Stock Options. (i) Except as set forth in
Section 2.03(a) and 2.03(b), upon the exercise of any option to purchase
Distributing stock (whether before or following the Distribution), Distributing
shall claim any tax deduction attributable to such exercise on its Tax Return
and Controlled shall not claim such deduction on its Tax Return, and (ii) upon
the exercise of any option to purchase Controlled stock following the
Distribution, Controlled shall claim any tax deduction attributable to such
exercise on its Tax Return and Distributing shall not claim such deduction on
its Tax Return.

                  (d) Definitions. For purposes of this Section 2.03, the
following terms

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shall have the following meanings:

                  (i) An "Acquired Company Option" shall mean any option to
                          -----------------------
purchase Distributing stock held by a Controlled Employee (as defined below)
granted under (1) the Medco Containment Services, Inc. 1991 Class C
Non-Qualified Stock Option Plan (as amended effective November 18, 1993), (2)
the Systemed, Inc. 1993 Employee Stock Option Plan, (3) the ProVantage Health
Services, Inc. 1999 Stock Incentive Plan, (4) the Medical Marketing Group, Inc.
1991 Class B Stock Option Plan and (5) the Medical Marketing Group, Inc. 1991
Special Non-Qualified Stock Option Plan.

                  (ii) The "Controlled Employees" shall mean any and all
                            --------------------
employees of the "Medco Group" (as defined in the Distribution Agreement)
immediately following the Distribution.

                  (iii) A "Merck Option" shall mean any option to purchase
                           ------------
Distributing stock held by a Controlled Employee granted prior to February 26,
2002, other than the Acquired Company Options.

                  (iv) The "Option Tax Value" as to the exercise of any option
                            ----------------
shall be an amount equal to the sum of (1) the amount of the deduction which
would have been realized by Distributing thereon if Distributing had claimed
such deduction multiplied by the highest statutory federal income tax rate to
which Distributing is subject in the year of exercise (regardless of actual
liability), plus (2) the amount of the deduction which would have been realized
by Distributing thereon if Distributing had claimed such deduction multiplied by
Distributing's weighted average state statutory income tax rate in

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the year of option exercise (regardless of actual liability, but less federal
benefit), plus (3) employment taxes, if any, payable by Distributing by reason
of the exercise of such option, plus (4) an additional payment such that, after
payment by Distributing of Tax, if any, upon the receipt of the Option Tax Value
(including upon the payment provided by this clause (4)), Distributing retains
an amount equal to the sum of the amounts set forth in clauses (1), (2) and (3)
of this sentence.

         2.04     Preparation of Tax Returns.
                  --------------------------

                  (a) Distributing shall cause the Controlled Group to join, for
any Post-Exchange Period for which the Controlled Group is required to do so
(and may cause the Controlled Group (or any member thereof) to join for any such
period or Tax Return for which the Controlled Group is eligible but not required
to do so), in all federal, state or local consolidated, combined or unitary
Income Tax Returns of Distributing's filing group. Distributing shall prepare
and timely file all such federal, state or local consolidated, combined or
unitary Tax Returns and shall timely pay all Tax with respect to such Tax
Returns. Distributing shall provide to Controlled a copy of the portion of each
such Tax Return and any supporting schedules that relate to the Controlled Group
within 5 days after the filing thereof. With respect to the Income Taxes payable
for the taxable year covered by such Tax Returns, Controlled shall pay to
Distributing, within 30 days following the close of such taxable year, the
current provision for such Income Taxes, as recorded on the financial statements
of Controlled. Within 30 days after the later of (i) the filing of the federal
Income Tax Return for such taxable year and (ii) the filing of the last to be
filed state Income Tax Return for such taxable year, Controlled shall pay to
Distributing, or Distributing shall pay to Controlled, as applicable, the amount
by which the Taxes paid pursuant to the previous sentence are less than (in the
case of a payment by Controlled) or more than (in the case of a payment by
Distributing) the sum of the Controlled Separate Federal Income Tax Liability
and Controlled Separate

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State Tax Liability.

                  (b) Distributing shall prepare (or cause to be prepared) and
Controlled shall timely file (or cause to be timely filed) any other Tax Return
relating to Income Tax of the Controlled Group for any period that begins before
the Distribution Date (or any portion of such a Tax Return which relates to the
portion of such period ending on the Distribution Date) whether it is required
to be filed before or after the Distribution Date (other than those required to
be filed by Distributing pursuant to Section 2.04(a) above). Distributing shall
provide a copy of each such Tax Return (or portion thereof) and any supporting
schedules to Controlled at least 30 days before the date such Return is to be
filed by Controlled for Controlled's review and approval, which approval shall
not be unreasonably withheld. Controlled shall pay all Tax with respect to such
Tax Return, except that Distributing shall pay to Controlled at least 5 days
prior to the filing of such Tax Return the amount due on such Tax Return that is
the responsibility of Distributing pursuant to Section 2.01.

                  (c) The filing of Tax Returns relating to Other Controlled Tax
shall be governed by the Transition Services Agreement. Controlled shall pay all
Tax with respect to any such Tax Return.

                  (d) Controlled shall not file (or allow the Controlled Group
to file) any amended Tax Returns with respect to the Controlled Group for any
Pre-Exchange Period or Post-Exchange Period without Distributing's consent.

         2.05 Cooperation and Exchange of Information. Distributing, on the one
              ---------------------------------------
hand, and Controlled, on the other, will timely and competently provide each
other with such cooperation and information as either of them reasonably may
request of the other in (i) filing any Tax Return, amended return or claim for
refund, (ii) determining a liability for Tax or a right to a refund of Tax or
(iii) participating in or conducting any audit or other proceeding in respect of
Tax. Such cooperation and information shall include providing

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copies of relevant Tax Returns or portions thereof, together with accompanying
schedules and related work papers and documents relating to rulings or other
determinations by any Tax Authorities. Each party shall devote the personnel and
resources necessary in order to carry out this Section 2.05 and shall make its
employees available on a mutually convenient basis to provide explanations of
any documents or information provided hereunder. Except as provided to the
contrary in the Transition Services Agreement, each party shall carry out their
responsibilities under this Section 2.05 without charge to the other. Any
information obtained under this Section 2.05 shall be kept confidential, except
as may be otherwise necessary in connection with the filing of Tax Returns or
claims for refund or in conducting an audit or other proceeding.

         2.06     Tax Contests.
                  ------------

                  (a) Notice. Each of the parties shall provide prompt notice to
the other party of any pending or threatened Tax audit, assessment or proceeding
or other Tax Contest of which it becomes aware related to Tax for which it is
indemnified by the other party hereunder. Such notice shall contain factual
information (to the extent known) describing any asserted Tax liability in
reasonable detail and shall be accompanied by copies of any notice and other
documents received from any Tax Authority in respect of any such matters. If an
indemnified party has knowledge of an asserted Tax liability with respect to a
matter for which it is to be indemnified hereunder and such party fails to give
the indemnifying party prompt notice of such asserted Tax liability, then (i) if
the indemnifying party is precluded from contesting the asserted Tax liability
in any forum as a result of the failure to give prompt notice, the indemnifying
party shall have no obligation to indemnify the indemnified party for any Tax
arising out of such asserted

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Tax liability, and (ii) if the indemnifying party is not precluded from
contesting the asserted Tax liability in any forum, but such failure to give
prompt notice results in a monetary detriment to the indemnifying party, then
any amount which the indemnifying party is otherwise required to pay the
indemnified party pursuant to this Agreement shall be reduced by the amount of
such detriment.

                  (b) Control of Tax Contests. Each Company shall have full
responsibility and discretion in handling, settling or contesting any Tax
Contest involving a Tax for which it is liable pursuant to Section 2 of this
Agreement; provided, however, Distributing shall have full responsibility and
discretion in handling, settling or contesting any Tax Contest with respect to a
consolidated, combined or unitary federal or state Income Tax of which
Distributing or a Distributing Subsidiary is the common parent. Furthermore,
Distributing may participate in any Tax Contest with respect to Covered
Transaction Tax (as hereinafter defined), and Controlled shall consider in good
faith Distributing's advice with respect thereto, regardless of whether
Distributing has liability or indemnification obligations with respect to such
Tax under this Agreement.

                                   ARTICLE III

                                TRANSACTIONS TAX

         3.01     Transactions Tax.
                  ----------------

                  (a) General. Except as otherwise provided in this Section
3.01, Distributing shall be responsible for and pay any and all Tax resulting
from income or gain recognized by Distributing as a result of the Distribution
failing to qualify for or maintain tax-free treatment pursuant to Section 355 of
the Code or other provisions of the Code or corresponding provisions of other
applicable Tax laws and any Tax resulting

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from any income or gain recognized by Distributing or its Affiliates (including
the Controlled Group) under Treasury Regulations Sections 1.1502-13 or 1.1502-19
(or any corresponding provisions of other applicable Tax laws) as a result of
the Distribution (collectively "Covered Transaction Tax").

                  (b) Inconsistent Acts and Events. Controlled shall be liable
for, and shall indemnify and hold harmless the Distributing Group from and
against any liability for, any Covered Transactions Tax (including without
limitation reasonable attorney fees and other costs incurred in connection
therewith) to the extent arising from (i) any breach by the Controlled Group of
the representations or covenants under Section 4, (ii) any Tainting Act (as
hereinafter defined) performed by the Controlled Group (whether or not Section
4.02(d) is complied with) and (iii) any Section 355(e) Event with respect to
Controlled (whether or not such event is caused by a Tainting Act). A Section
355(e) Event with respect to Controlled means any event, involving the stock of
Controlled or assets of the Controlled Group, which causes the Distribution to
be a taxable event to Distributing as the result of the application of Section
355(e) of the Code (i.e., the Distribution becomes taxable to Distributing under
Section 355(e) and but for the event the Distribution would not have been a
taxable event to Distributing under Section 355(e)).

                                   ARTICLE IV

                          REPRESENTATIONS AND COVENANTS

         4.01     Representations.
                  ---------------

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                  (a) Each of Controlled and Distributing represent that, as of
the date of this Agreement, it and its Affiliates know of no fact that would
jeopardize the expected Tax treatment of the Exchange and Distribution.

                  (b) Each of Controlled and Distributing represent and warrant
that neither it nor any of its Affiliates has any plan or intent to take any
action which is inconsistent with the expected Tax treatment of the Exchange and
the Distribution.

         4.02     Covenants.
                  ---------

                  (a) Controlled covenants and agrees that it will not take any
action, and it will cause its Affiliates to refrain from taking any action,
which is inconsistent with the expected Tax treatment of the Exchange and the
Distribution (any such action, including any action referred to in clause (i)
through (iii), is referred to in this Agreement as a "Tainting Act"). Without
limiting the foregoing:

                  (i) Specified Actions. During the two year period following
the Distribution Date, Controlled will not (and it will cause its Affiliates not
to) (A) liquidate, merge or consolidate with or into any other corporation; (B)
issue any of its capital stock in one or more transactions, other than issuances
of stock to employees or directors in connection with the performance of
services for Controlled (that are not excessive by reference to the services
performed) which issuances either are (x) with respect to the exercise of
options that were granted by Controlled before the Closing Date or (y) with
respect to the exercise of options that were granted by Controlled on or after
the Closing Date which satisfy the requirements of Treasury Regulations Section
1.355-7T(f)(6) to not be treated for purposes of Section 355(e) of the Code to
be part of a plan or series of related transactions that includes the
Distribution; (C) redeem, purchase or

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otherwise reacquire its capital stock in one or more transactions; (D) change
the voting rights of any of its stock; (E) sell, exchange, distribute or
otherwise dispose of, other than in the ordinary course of business, all or a
substantial part of the assets of any of the trades or businesses relied upon to
satisfy Section 355(b) of the Code; (F) issue any options to acquire Controlled
Shares other than options which satisfy the requirements of Treasury Regulations
Section 1.355-7T(g)(3)(ii); or (G) discontinue or cause to be discontinued the
active conduct of any of the trades or businesses relied upon to satisfy Section
355(b) of the Code.

                  (ii) No Inconsistent Actions. Regardless of any change in
circumstances, Controlled covenants and agrees that it will not take any action
(and it will cause its Affiliates to refrain from taking any action) which is
inconsistent with any factual statements or representations in the IRS Private
Letter Ruling on or before the second anniversary of the Distribution Date other
than as permitted in this Section 4. For this purpose an action is considered
inconsistent with a representation if the representation states that there is no
plan or intention to take such action.

                  (iii) 355(e) Covenant. Without in any manner limiting
paragraphs (i) or (ii) immediately above, Controlled covenants and agrees that,
through the second anniversary of the Distribution Date, it will not enter into
(and it will cause its Affiliates to refrain from entering into) any agreements,
understandings, arrangements or substantial negotiations with respect to
transactions or events (including stock issuances, option grants, capital
contributions, acquisitions, or changes in the voting power of any of its
stock), which may cause the Distribution to be treated as part of a plan
pursuant to

                                       19

<PAGE>

which one or more persons acquire directly or indirectly Controlled stock
representing a "50 percent or greater interest" within the meaning of Section
355(e)(4) of the Code.

                  (b) Amended or Supplemental Rulings. Each of Distributing and
Controlled covenants and agrees that it will not file, and it will cause its
Affiliates to refrain from filing, any amendment or supplement to the IRS
Private Letter Ruling with respect to the Distribution subsequent to the
Distribution Date without the consent of the other, which consent shall not be
unreasonably withheld.

                  (c) Each of Distributing and Controlled covenants and agrees
that it will not take, and it will cause its Affiliates to refrain from taking,
any position on a Tax Return that is inconsistent with the treatment of the
Distribution as tax-free pursuant to Code Section 355 and the treatment of the
Distribution in a manner inconsistent with the IRS Private Letter Ruling.

                  (d) Exceptions. Notwithstanding the foregoing, Controlled
shall be permitted to take an action inconsistent with Section 4.02(a), if,
prior to taking such action, Controlled provides notification to Distributing of
its plans with respect to such action, and promptly responds to any inquiries by
Distributing following such notification, and either:

                  (i) Controlled obtains a ruling with respect to the action
from the Internal Revenue Service or other applicable Tax Authority that is
reasonably satisfactory to Distributing (except that Controlled shall not submit
any such ruling request if Distributing determines in good faith that filing
such request might have a materially adverse effect upon Distributing), on the
basis of facts and representations consistent with the facts at the time of such
action, that such action will not affect the

                                       20

<PAGE>

expected Tax treatment of the Exchange and Distribution or the IRS Private
Letter Ruling,

                  (ii) Controlled obtains an unqualified opinion reasonably
acceptable to Distributing of an independent nationally recognized tax counsel
acceptable to Distributing, on the basis of facts and representations consistent
with the facts at the time of such action, that such action will not affect the
Tax treatment of the Distribution or the IRS Private Letter Ruling, or

                  (iii) Distributing consents in writing to such action, which
consent shall be granted or withheld in the sole and absolute discretion of
Distributing.

         Notwithstanding anything to the contrary in this Agreement, Controlled
shall be liable for, and shall indemnify and hold harmless Distributing from any
Covered Transaction Tax resulting from a Tainting Act by Controlled or its
Affiliates, regardless of whether the exception of this Section 4.02(d) is
satisfied with respect to such act.

                                       21

<PAGE>

                                    ARTICLE V

                            MISCELLANEOUS PROVISIONS

         6.01 Notice. Any payment, notice or communication required or permitted
              ------
to be given under this Agreement shall be in writing (including facsimile) and
mailed, faxed or delivered to the parties at the following addresses (or at such
other address as one party may specify by notice to the other party):

                  if to Distributing:

                           Merck & Co., Inc.
                           One Merck Drive
                           P.O. Box 100
                           Whitehouse Station, New Jersey 08889
                           Attention: Tax Director

                  if to Controlled:

                           MedcoHealth Solutions, Inc.
                           100 Parsons Pond Drive
                           Franklin Lakes, New Jersey  07417
                           Attention: Tax Director

              Notification of a change of address shall be given by either
party to the other as provided in this Section 6.01. All such notices and
communications shall be effective (i) when received, if mailed or delivered, or
(ii) when confirmed by fax answerback, if faxed.

         6.02 Governing Law. This Agreement shall be governed by the laws
              -------------
applicable to contracts entered into and to be performed within the State of New
Jersey.

         6.03 Dispute Resolution. Any and all disputes between Distributing and
              ------------------
Controlled arising out of any provision of this Agreement shall be submitted to
and

                                       22

<PAGE>

resolved by an independent nationally recognized accounting firm selected by
Distributing and Controlled.

         6.04 Jurisdiction. Each party agrees to submit itself exclusively to
              ------------
the personal jurisdiction of any New Jersey court in the event any dispute
arises out of this Agreement or any of the transactions contemplated by this
Agreement and agrees that it will not attempt to deny or defeat such personal
jurisdiction or venue by motion or other request for leave from any such New
Jersey court. Each party further agrees that service of any process, summons,
notice or document by U.S. registered mail to such party's respective address
set forth above shall be effective service of process for any action, suit or
proceeding in New Jersey with respect to any matters to which it has submitted
to jurisdiction in this Section 6.04.

         6.05 Waiver Of Jury Trial. Each party waives, to the fullest extent
              --------------------
permitted by applicable law, any right it may have to a trial by jury in respect
of any dispute arising out of this Agreement.

         6.06 Entire Agreement. This Agreement embodies the entire understanding
              ----------------
between the parties relating to its subject matter and supersedes and terminates
all prior agreements and understandings among the parties with respect to such
matters. No promises, covenants or representations of any kind, other than those
expressly stated herein, have been made to induce any party to enter into this
Agreement. This Agreement shall not be modified or terminated except by a
writing duly signed by each of the parties hereto, and no waiver of any
provisions of this Agreement shall be effective unless in a writing duly signed
by the party sought to be bound. If, and to the extent, the provisions of this
Agreement conflict with the Distribution Agreement, or any other agreement

                                       23

<PAGE>

entered into in connection with the Distribution the provisions of this
Agreement shall control.

         6.07 Assignment; Binding Effect. Neither this Agreement nor any of the
              --------------------------
rights, interests or obligations under this Agreement shall be assigned, in
whole or in part, by operation of law or otherwise by any of the parties without
the prior written consent of the other party; provided, however, that no such
consent shall be required in the event of a merger, consolidation or sale of
either Distributing or Controlled. Subject to the preceding sentence, this
Agreement shall be binding on, and shall inure to the benefit of, and be
enforceable by, the parties hereto and their respective successors and assigns.

         6.08 Counterparts. This Agreement may be executed in two or more
              ------------
counterparts, each of which shall be deemed to be an original, but all of which
together shall constitute one and the same.

         6.09 Severability. If any provision of this Agreement or the
              ------------
application of any such provision to any person or circumstances shall be held
invalid, illegal, or unenforceable in any respect by a court of competent
jurisdiction, such invalidity, illegality, or unenforceability shall not affect
any other provision hereof.

         6.10 Headings. Headings of sections in this Agreement are inserted for
              --------
convenience of reference only and are not intended to be a part of or to affect
the meaning or interpretation of this Agreement.

         6.11 Survival. Notwithstanding anything in this Agreement to the
              --------
contrary, the provisions of this Agreement shall survive for thirty days after
the full period of all applicable statutes of limitations (giving effect to any
waiver, mitigation or extension thereof).

                                       24

<PAGE>

         IN WITNESS WHEREOF, each of the parties has caused this Agreement to be
executed by its respective duly authorized officer as of the date first set
forth above.

         MERCK & CO., INC.                           MEDCOHEALTH SOLUTIONS, INC.

         By:                                         By:
         Name:                                       Name:
         Title:                                      Title:

                                       25<PAGE>

                                                                Exhibit 10.9
                                                                ------------

                                     FORM OF

                      PATIENT ASSISTANCE PROGRAM AGREEMENT

                                     BETWEEN

                             MERCK & CO., INC.

                                       AND

                      MERCK-MEDCO MANAGED CARE, L.L.C.

<PAGE>

                      PATIENT ASSISTANCE PROGRAM AGREEMENT

     THIS PATIENT ASSISTANCE PROGRAM AGREEMENT (this "Agreement"), dated as of
_______, 2002, between Merck & Co., Inc., a New Jersey corporation ("Merck"),
and Merck-Medco Managed Care, L.L.C., a Delaware limited liability company
("Medco"; Merck and Medco each being referenced herein individually as a
"Party," and collectively as the "Parties"). Capitalized terms used herein but
not otherwise defined herein shall have the meaning ascribed to such terms in
the Master Separation and Distribution Agreement to be entered into between the
Parties.

          WHEREAS, the Board of Directors of Merck has determined that it is
appropriate and desirable for Merck to separate the Medco Group from the Merck
Group (the "Separation");

          WHEREAS, in connection with the foregoing, Merck and Medco intend to
enter into a Master Separation Agreement, which will provide, among other
things, for the conversion of Medco to a Delaware corporation named MedcoHealth
Solution, Inc. (the "Conversion"), the Separation, the IPO of Medco Common
Stock, the declaration of the Merck Dividend immediately after the IPO Closing
Date, the subsequent Distribution of all the Medco Common Stock then owned by
Merck to the holders of Merck common stock, and the execution and delivery of
certain other agreements in order to facilitate and provide for the foregoing;

          WHEREAS, Merck has instituted a Patient Assistance Program (the
"General Program") to help provide access to Merck Products (other than
Crixivan(R)), and a separate Patient Assistance Program (the "Crixivan(R)
Program," together with the General Program, the "Programs") to help provide
access to Crixivan(R), for patients with medical needs who lack prescription
coverage and cannot afford drug treatment;

          WHEREAS, Merck desires that Medco, dispense, through one or more of
its pharmacies, as provided herein, Merck Products, including Crixivan(R), by
mail in connection with the Programs;

<PAGE>

          WHEREAS, Medco and Merck have developed an electronic feed between the
Nominated Agent (defined below) for the General Program and Medco pursuant to
which such Nominated Agent may electronically transmit to Medco eligibility
information with respect to patients under the General Program (the "Eligibility
Electronic Feed"); and

          WHEREAS, also as part of the foregoing, the parties further desire to
enter into this Agreement to set forth Medco's obligation with respect to the
Programs.

          NOW, THEREFORE, in consideration of the foregoing and the covenants
and agreements set forth below, the parties hereto agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

     For the purpose of this Agreement, the following capitalized terms shall
have the following meanings:

     1.1 Ancillary Agreements. "Ancillary Agreements" shall have the
meaning set forth in the Master Separation and Distribution Agreement.

     1.2 Confidential Disclosure Agreement. "Confidential Disclosure
Agreement" shall mean that certain Confidential Disclosure Agreement to be
entered into between the Parties.

     1.3 "Dispensing Pharmacies" shall mean mail order pharmacies of Medco
located in the U.S. from which the Merck Products shall be dispensed in
accordance with Article II.

     1.4 Effective Date. "Effective Date" shall mean the date hereof.

     1.5 Expiration Date. "Expiration Date" shall have the meaning set
forth in Article 10.

     1.6 Master Separation Agreement. "Master Separation Agreement" shall
mean that certain Master Separation and Distribution Agreement dated as of
the date hereof, between the Parties.

     1.7 Merck Products. "Merck Products" means pharmaceutical products
(including Crixivan(R)), other than injectables and vaccines, that (w) are
manufactured by Merck or any of its Subsidiaries, (x) have been approved or
recommended by the U.S. Food and Drug Administration, (y) may be dispensed only
pursuant to a Prescription under applicable law and (z) are subject to an
effective patent granted by the U.S. Patent and Trademark Office.

     1.8 Nominated Agent. "Nominated Agent" shall mean one or more third
party vendor from time to time employed by Merck to administer the initial
application receipt, application review, general program eligibility
determination, and patient enrollment functions of the Programs. The Nominated
Agent for the General Program is currently TeleRx Marketing Inc. The Nominated
Agent for the Crixivan(R) Program is currently the Lash Group. Merck shall have
the right to replace Nominated Agents or appoint additional Nominated Agents for
all or any portion of either of the Programs. Merck shall provide Medco with
reasonable advance notice of any anticipated appointed of a new Nominated Agent
to allow Medco to develop appropriate operational links with such Nominate Agent
to insure continuous service for the Programs.

     1.9 Person. "Person" means any individual, corporation, association,

<PAGE>

partnership (general or limited), joint venture, trust, estate, limited
liability company, or other legal entity or organization.

     1.10 Prescription. "Prescription" means a valid and legal order to
dispense a Merck Product.

     1.11 Programs. "Programs" shall have the meaning set forth in the
Recitals.

     1.12 Subsidiary. "Subsidiary" of either Party means a corporation or other
organization whether incorporated or unincorporated, of which at least a
majority of the securities or interests having by the terms thereof ordinary
voting power to elect at least a majority of the board of directors or others
performing similar functions with respect to such corporation or other
organization is directly or indirectly owned or controlled by such Party or by
any one or more of its Subsidiaries, or by such Party and one or more of its
Subsidiaries. For purposes of this Agreement, neither Medco nor any of its
Subsidiaries shall be deemed to be a Subsidiary of Merck.

     1.13 "Term" shall have the meaning set forth in Section 2.6.

                                   ARTICLE II

                                    SERVICES

     During the Term, Medco shall provide, the following services with respect
to the Programs:

     2.1 Patient Enrollment. Receipt of the initial applications with respect to
each of the Programs, and application review, general program eligibility
determination and enrollment functions with respect to each Program, shall be
the responsibility of the applicable Nominated Agent.

     2.2 Prescriptions For the General Program. (a) The Nominated Agent for the
General Program will be responsible for sending to Medco eligibility and
Prescription information with respect to patients eligible to participate in the
General Program. Eligibility information with respect to the General Program
shall be sent to Medco by the Nominating Agent through the Eligibility
Electronic Feed. On the day that any eligibility information is sent through the
Eligibility Electronic Feed, the Nominated Agent shall either (1) send the
original prescription form via Federal Express (or other comparable overnight
courier providing a traceable, secure method of shipment) for receipt by Medco
at a Dispensing Pharmacy (the address of which shall be provided to the
Nominated Agent by Medco) on the following day or (2) send a copy of the
original prescription form to Medco pursuant to the Faxable Application Process
(as defined in Section 2.5 below). Refill requests under the General Program may
be made by the patient or prescribing physician using a toll free number
established by Medco or by mail (it being understood that patients and
physicians will be discouraged from making refill requests by mail). When Medco
has received all eligibility and Prescription information with respect to a
Prescription or any request for a refill in accordance with the foregoing, Medco
shall cause a Dispensing Pharmacy to dispense the Merck Product covered by such
Prescription (or refill) as written (subject to the next sentence) from such
pharmacy's stock of such Merck Product, by mailing such Merck Products via
Federal Express (or other comparable courier providing a traceable, secure
method of shipment), two (2) day ground, directly to the patient or, at the
physician's request (as set forth in the applicable application form), directly
to the patient's physician's office. Prescriptions under the General Program may
provide for up to a 90-day supply at a time with up to three refills each with
up to a 90-day supply.

<PAGE>

     (b) In addition to providing services with respect to the General Program
as otherwise provided in this Agreement, Medco shall continue to provide
services with respect to the General Program in accordance with the Memorandum
of Understanding between the Parties, effective April 1, 1996, relating to the
General Program from the date hereof until June 30, 2002; provided that the fees
and reimbursement amounts payable to Medco for providing such services shall be
determined in accordance with Article 3 of this Agreement.

     2.3 Prescriptions for the Crixivan(R) Program. The Nominated Agent for the
Crixivan(R) Program will be responsible for sending to Medco hard-copy paper
eligibility and Prescription information with respect to patients eligible to
participate in the Crixivan(R) Program. The parties shall cooperate to maintain
a 24-hour turn-around time for this transfer of such information. Such
information shall be sent via any traceable, secure method to a Dispensing
Pharmacy (the address of which shall be provided to the Nominated Agent by
Medco). Refill requests under the Crixivan(R) Program may be made by
transmitting a refill request, including the patients' name and ID (and Social
Security number and Prescription number, if available), to Medco by facsimile
(to a facsimile number specified by Medco. When Medco has received all
eligibility and Prescription information (including the original Prescription
form) with respect to a Prescription or any request for a refill for Crixivan(R)
in accordance with the foregoing, Medco shall cause a Dispensing Pharmacy to
dispense the Crixivan(R) covered by such Prescription (or refill) as written
(subject to the next sentence) from such pharmacy's stock of Crixivan(R), by
mailing such Merck Products via Federal Express (or other comparable courier
providing a traceable, secure method of shipment), two (2) day ground, directly
to the patient or, at the physician's request (as set forth in the applicable
application form), directly to the patient's physician's office. Prescriptions
under the Crixivan(R) Program may provide for up to a 90-day supply at a time
with up to three refills each with up to a 90-day supply.

     2.4 Prescription Volume; Design Changes. (a) Merck shall use
commercially reasonable efforts to provide to Medco monthly Merck's good
faith estimate of anticipated Prescription volume under the General Program
and the Crixivan(R) Program for the following six-month period. If any such
estimate provided by Merck anticipates that the compounded volume growth of
the General Program and the Crixivan(R) Program will exceed the compounded
volume growth for such Programs estimated as of the date hereof by the Parties,
Medco will provide to Merck Medco's good faith estimate of any capital
expenditures Medco will be required to make for the purpose of providing
services hereunder with respect to the Programs. After Medco's delivery of such
estimate to Merck, the parties shall negotiate in good faith with the goal of
agreeing on the specific amount of capital expenditures Medco will be required
to make that is allocable to that portion of the anticipated compounded volume
growth for the General Program and the Crixivan(R) Program that exceeds the
compounded volume growth for such Programs estimated as of the date hereof by
the Parties (the "Anticipated Excess Volume"). Merck agrees to reimburse Medco
for the capital expenditures incurred by Medco in accordance with a budget
approved by Merck setting forth the amounts of capital expenditures allocable to
the Anticipated Excess Volume.

     (b) In the event that at any time during the Term, Merck proposes to
implement material changes to the design of the Programs (other than increases
in volume under the Programs, which shall be subject to Section 2.4(a)), Merck
shall provide to Medco a written notice describing such proposed design changes
in reasonable detail. Within 20 days after its receipt of such notice, Medco
will provide to Merck Medco's good faith estimate of any of the out-of-pocket
expenses Medco will be required to incur to implement the proposed design
changes. After Medco delivers such

<PAGE>

estimate to Merck, the parties shall negotiate in good faith with the goal of
agreeing on a budget for the out-of-pocket expenses to be incurred by Medco to
implement the proposed design changes (a "Design Change Budget"). Medco shall
implement the proposed design changes in accordance with a Design Change Budget
agreed by the parties as promptly as practicable after Merck and Medco reach
agreement thereon. Merck shall reimburse Medco for the out-of-pocket expenses
incurred by Medco in connection with the implementation of the proposed design
changes in accordance with the agreed-upon Design Change Budget.

     (c) Each party shall designate one or more representatives to communicate
with the designated representatives of the other with respect to the subject
matter of this Section 2.4. The parties shall provide each other with the names
and contact information of their designated representatives.

     2.5 Additional Services. In relation to the General Program (but not
the Crixivan Program), Medco shall:

     o    provide a data entry function for each Prescription verifying such
          Prescription against eligibility information received from the
          Nominated Agent through the Electronic Feed;

     o    engage in ongoing support interactions with physicians in respect of
          the General Program to ensure that the Merck Products subject to the
          General Program can be dispensed;

     o    capture all information on Prescriptions that have been fulfilled on a
          claims file using Medco's standard record layout and electronically
          provide such data to the Nominated Agent according to Medco's standard
          bi-weekly billing cycle;

     o    in the period between Medco receiving each electronic eligibility
          file and Prescription from the Nominated Agent and Medco supplying the
          Nominated Agent with a claims file tape, maintain a status inquiry
          support capability (or receive transferred calls from patients
          directly from the Nominated Agent to check actual prescription
          dispensing status) so that the Nominated Agent can access information
          with respect to any application;

     o    maintain an automated Prescription refill service allowing
          patients and prescribing physicians to order permissible refills
          using a toll free number established for that purpose (the
          "Automated Refill Service"). The Automated Refill Service shall
          provide for a refill process agreed upon by the parties; provided
          that such process shall employ the use of all applicable
          technologies available to Medco (to the extent technologically
          feasible), and Medco shall use commercially reasonable efforts to
          ensure that such process maximizes time efficiencies and savings
          for Merck; and

     o    develop and incorporate technology to enable Medco to support a
          process for receipt by facsimile from the Nominated Agent of
          Prescription information (the "Faxable Application Process"), as
          promptly as practicable (but in any event within 90 days) of the
          Nominated Agent and Medco reaching agreement with respect to the
          detailed design and technical architecture for the Faxable
          Application Process. Medco shall use commercially reasonable
          efforts to reach such agreement with the Nominated Agent as
          promptly as practicable after the date of this Agreement.

     2.6 Term. This Agreement shall remain in effect from the Effective Date
through the Expiration Date (the "Term"). The "Expiration Date" shall

<PAGE>

be December 31, 2006; provided that in the event of the early termination of
this Agreement in accordance with Article V, the date of such early termination
shall be "Expiration Date".

                                   ARTICLE III

                                  COMPENSATION

     3.1 Charges. For the services provided by Medco to Merck hereunder,
Merck shall pay Medco the fees, and reimburse Medco for its expenses, as
set forth on Schedule 3.1

     3.2 Payment Terms. Merck shall pay and reimburse Medco in accordance with
Section 3.1 for the services provided hereunder during each fiscal month of
Medco during the Term, within thirty (30) days after a receipt of an invoice
therefor (accompanied by such documentation verifying the charges reflected
thereon as shall be reasonably requested by Merck).

                                   ARTICLE IV

                               GENERAL PROVISIONS

     4.1 Parameters. Medco shall, and shall cause to be provided, the services
under this Agreement in the manner in which such services were provided prior to
the date of this Agreement (or in a manner that is more technologically
advanced, or efficient).

     4.2 Good Faith Cooperation; Consents. The Parties will use good faith
efforts to cooperate with each other in all matters relating to the provision
and receipt of the services to be provided hereunder. Such cooperation shall
include exchanging information, and obtaining all third party consents,
authorizations, licenses, sublicenses or approvals necessary to permit each
Party to perform its obligations hereunder (including by way of example, not by
way of limitation, rights to use third party software needed for the performance
of services hereunder). Each Party will maintain, in accordance with its
standard document retention procedures, documentation supporting the information
relevant to cost calculations and cooperate with each other in making such
information available as needed in the event of a tax or regulatory audit,
whether in the United States or any other country.

     4.3 Promotional Materials. Merck shall have sole responsibility for
preparing and distributing all promotional materials relating to the Programs,
and the cost of preparing and distributing such materials shall be borne by
Merck. No Medco Party may prepare or distribute any promotional materials
relating to any Program without Merck's consent. Merck shall provide Medco with
an opportunity to review and comment on promotional materials with respect to
the Programs to be disseminated by Merck prior to the public dissemination
thereof. Merck shall use commercially reasonable efforts to provide a draft of
any such promotional materials to Medco at lease 30 days prior to the public
dissemination thereof.

     4.4 Medco Participation. The Parties acknowledge Medco has not participated
in, and shall not participate in the design of the Program relative to financial
criteria, patient selection, etc. Medco has assisted in the design of dispensing
technology and automated process design to administer the Patient Assistance
Program.

     4.5 Information. Any information or data generated by any Medco Party in
connection with its services hereunder ("Program Information") shall be the
property of Merck and shall not be disclosed or shared by any Medco Party with
any Person except as permitted by Merck, provided that information concerning
the dispensing of prescription drugs customarily

<PAGE>

maintained by Medco shall be maintained by Medco and may be disclosed by Medco
to regulatory agencies having jurisdiction or as otherwise required under
applicable laws or regulations. Medco shall disclose Program Information to
third-parties to the extent requested by Merck. No Medco Party shall use Program
Information for purposes other than patient care in connection with the
Programs.

                                    ARTICLE V

                                EARLY TERMINATION

     5.1 Early Termination. Merck may terminate this Agreement any time upon
sixty- (60) days prior written notice to Medco. Either party may terminate this
Agreement if the other breaches in any material respect any of its obligations
hereunder and does not cure such breach hereunder within thirty (30) days after
being notified of such breach.

     5.2 Survival. Those Sections of this Agreement that, by their nature, are
intended to survive termination will survive in accordance with their terms.

                                   ARTICLE VI

                                 CONFIDENTIALITY

     Without limiting the obligations of the Parties under this Agreement, the
terms of the Confidential Disclosure Agreement shall apply to any Confidential
Information (as defined in that Agreement) of either Party provided to the other
Party for the purpose of providing services under this Agreement.

                                   ARTICLE VII

                                 PATIENT PRIVACY

     7.1 Medco Obligations. Medco represents and warrants and agrees that it
will perform all of its duties under this Agreement in compliance with all
applicable federal, state, local and foreign laws and regulations and licensing
requirements, including but not limited to those related to patient
notification, authorization and consent, privacy of medical records and medical
information. By way of example, Medco is required under the Standards adopted
pursuant to the Health Insurance Portability and Accountability Act of 1996,
either directly as a covered entity or in its role as a business associate of
its health plan clients, to assure that protected health information (all as
defined in such Standards) is used or disclosed only in accordance with such
Standards. If at any time during the Term, Medco concludes that it cannot
perform one or more obligations under this Agreement because of legal or
regulatory restrictions imposed upon it, Medco shall promptly notify Merck,
explain why it believes it cannot legally perform the obligation, and provide
Merck with an estimate of the impact of the restriction on its performance of
this Agreement as a whole. Nothing in this Agreement is intended to allow Medco
to create by contract an impediment to performance of this Agreement that
differs from any restriction to which Medco is subject as to either drug
manufacturers generally or any broader category of third parties.

     7.2 Merck Obligations. Merck represents, warrants and agrees that the data
provided by Merck to Medco pursuant to this Agreement shall not violate the
privacy and/or security rights of any third party or individual and that such
data shall be provided by Merck in compliance with the applicable rules and
regulations governing the use of data, including but not limited to, rules and
regulations governing the use of patient medical information. Merck further
represents, warrants and agrees that prior to

<PAGE>

providing any such data to Medco it will have obtained any and all necessary
consents or authorizations required for Merck to provide the data to Medco.

                                  ARTICLE VIII

                        RELATIONSHIP BETWEEN THE PARTIES

     The relationship between the Parties established under this Agreement is
that of independent contractors and neither Party is an employee, agent,
partner, or joint venture of or with the other.

                                   ARTICLE IX

                               DISPUTE RESOLUTION

     ANY DISPUTE, CONTROVERSY OR CLAIM BETWEEN THE PARTIES HERETO ARISING OUT OF
OR RELATING TO THIS AGREEMENT, INCLUDING, WITHOUT LIMITATION, DISPUTES
CONCERNING THE VALIDITY, INTERPRETATION OR PERFORMANCE OF OR UNDER THIS
AGREEMENT OR ANY TERM OR PROVISION HEREOF, SHALL BE EXCLUSIVELY GOVERNED BY AND
SETTLED IN ACCORDANCE WITH THE PROVISIONS OF ARTICLE III OF THE INDEMNIFICATION
AGREEMENT.

                                    ARTICLE X

                                  MISCELLANEOUS

     10.1 Press Releases. Merck shall use commercially reasonable efforts to
provide Medco with notice of, and an opportunity to review, any press release
relating to any of the Programs that Merck prior to the release thereof. Medco
shall not make any public statement with respect to any of the Programs without
the prior approval of Merck.

     10.2 Entire Agreement. This Agreement, the Separation Agreement and the
other Ancillary Agreements and the Exhibits, Annexes and Schedules referenced or
attached hereto and thereto constitute the entire agreement between the Parties
with respect to the subject matter hereof and thereof and shall supersede all
prior written and oral and all contemporaneous oral agreements and
understandings with respect to the subject matter hereof and thereof.

     10.3 Governing Law; Forum. This Agreement shall be construed in accordance
with, and all Disputes hereunder shall be governed by, the procedural (except to
the extent inconsistent with the procedures set forth in Article III of the
Indemnification Agreement) and substantive laws of the State of New York as to
all matters regardless of the laws that might otherwise govern under principles
of conflicts of laws applicable thereto. Under no circumstances may any party
seek or be awarded punitive damages under this Agreement. Any state court
sitting in New York county, New York and/or the United States District Court for
the Southern District of New York shall have exclusive jurisdiction and venue,
and each party hereto hereby submits to such jurisdiction and venue and
irrevocably waives, to the fullest extent permitted by applicable law, any
objection it may now or hereafter have to such jurisdiction or the laying of
such venue over any Disputes between the parties that are permitted to be
brought in a court, or the enforcement of any decision of an arbitrator,
pursuant to Article III of the Indemnification Agreement. Each of the parties
hereby irrevocably waives any right to a jury trial with respect to a Dispute.

     10.4 Notices. Except as expressly provided herein, all notices and other
communications required or permitted to be given by either Party pursuant to the
terms of this Agreement shall be in writing to and shall be deemed to have been
duly given when delivered in person, by express or

<PAGE>

overnight mail delivery by a nationally recognized courier (delivery charges
prepaid), or by registered or certified mail (postage prepaid, return receipt
requested), as follows:

               if to Merck:

                                     Merck & Co., Inc.
                                     One Merck Drive
                                     P.O. Box 100
                                     Whitehouse Station, New Jersey 08889
                                     Attention: General Counsel

               if to Medco:

                                     MedcoHealth Solutions, Inc.
                                     100 Parsons Pond Road
                                     Franklin Lakes, New Jersey  07417
                                     Attention: General Counsel

or to such other address as the Party to whom notice is given may have
previously furnished to the other in writing in the manner set forth above. All
notices and other communication shall be deemed to have been given and received
on the date of actual delivery.

     10.5 Binding Effect; Assignment; Third-Party Beneficiaries. Medco may not,
directly or indirectly, in whole or in part, whether by operation of law or
otherwise, assign or transfer this Agreement or its rights or obligations
hereunder, without Merck's prior written consent and, except as otherwise
permitted hereby, any attempted assignment, transfer or delegation without such
prior written consent shall be voidable at the sole option of Merck. Nothing in
this Agreement shall restrict any transfer of this Agreement by Merck, whether
by operation of law or otherwise. Without limiting the foregoing, this Agreement
shall be binding upon Merck and the other members of the Merck Group and Medco
and the other members of the Medco Group and their respective legal
representatives, successors and permitted assigns, and nothing in this
Agreement, express or implied, is intended to confer upon any other Person any
rights or remedies of any nature whatsoever under or by reason of this
Agreement.

     10.6 Offset. In addition to, and not in limitation of, any other remedies
any member of the Merck Group or any Merck Indemnitee (as defined in the
Indemnification Agreement) may be entitled to under the Separation Agreement,
any Ancillary Agreement (including this Agreement) or any Intercompany Agreement
(as defined in the Indemnification Agreement) , any member of the Merck Group or
any Merck Indemnitee may satisfy any amounts owed to such member of the Merck
Group or Merck Indemnitee by any member of the Medco Group by means of an offset
against any amounts any member of the Merck Group may from time to time owe to
any member of the Medco Group or an Medco Indemnitee, whether under the
Separation Agreement, any Ancillary Agreement (including this Agreement), any
Intercompany Agreement, any other agreement or arrangement existing between any
member of the Merck Group and any member of the Medco Group, or otherwise.

     10.7 Severability. If any term or other provision of this Agreement or any
Annexes, Schedules or Exhibits attached hereto is determined by a court,
administrative agency or arbitrator to be invalid, illegal or incapable of being
enforced by any rule of law or public policy, all other conditions and
provisions of this Agreement will nevertheless remain in full force and effect
so long as the economic or legal substance of the transactions contemplated
hereby is not affected in any manner materially adverse to any party hereto.
Upon such determination that any term or other provision is invalid, illegal or
incapable of being enforced, the parties hereto shall negotiate in good faith to
modify this Agreement so as to

<PAGE>

effect the original intent of the parties hereto as closely as possible in an
acceptable manner to the end that transactions contemplated hereby are fulfilled
to the fullest extent possible. If the parties are unable to reach an agreement
on any such modification, the arbitrator selected in accordance with Article III
of the Indemnification Agreement shall have the authority to determine such
modification.

     10.8 Failure or Indulgence Not Waiver. No failure or delay on the part of
any party hereto in the exercise of any right hereunder shall impair such right
or be construed to be a waiver of, or acquiescence in, any breach of any
representation, warranty or agreement herein, nor shall any single or partial
exercise of any such right preclude other or further exercise thereof or of any
other right.

     10.9 Amendment. No change or amendment will be made to this Agreement
except by an instrument in writing signed on behalf of each of the parties to
this Agreement.

     10.10 Interpretation. The headings contained in this Agreement, in any
Annex, Exhibit or Schedule hereto and in the table or contents to this Agreement
are for reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement. Any capitalized term used in any Annex,
Schedule or Exhibit but not otherwise defined therein, shall have the meaning
assigned to such term in this Agreement. When a reference is made in this
Agreement to an Article or Section, or an Annex, Exhibit or Schedule, such
reference shall be to an Article or Section of, or an Annex, Exhibit or Schedule
to, this Agreement unless otherwise indicated.

     10.11 Counterparts. This Agreement, including any Annexes, Schedules and
Exhibits hereto, and the other documents referred to herein, may be executed in
counterparts, each of which shall be deemed to be an original but all of which
shall constitute one and the same agreement.

     10.12 Reexecution. Medco shall reexecute and deliver this Agreement
after the Conversion and prior to the consummation of the IPO.

     10.13 Memoranda of Understandings. The Parties agree and acknowledge that,
subject to Section 2.2(b) this Agreement, shall supercede and replace in its
entirety the Memoranda of Understandings between the Parties regarding the
Programs.

     10.14 Indemnification Agreement. The indemnification obligation of the
Parties with respect to this Agreement shall be as set forth in the
Indemnification Agreement to be entered into between the Parties in connection
with the IPO.

     IN WITNESS WHEREOF, each of the Parties has caused this Agreement to be
executed in duplicate originals by its duly authorized representatives.

MERCK & CO., INC.                       MERCK-MEDCO MANAGED CARE, L.L.C

By:                                     By:
      ------------------------------         ----------------------------
Name:                                   Name:
Title:                                  Title:

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