Document:

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                                                                     EXHIBIT 4.2

                                                                  CONFORMED COPY

                  STOCKHOLDER AND REGISTRATION RIGHTS AGREEMENT

                                     BETWEEN

                              EXPRESS SCRIPTS, INC.

                                       AND

                         NEW YORK LIFE INSURANCE COMPANY

                           DATED AS OF OCTOBER 6, 2000
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                                TABLE OF CONTENTS

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RECITALS ............................................................................................1

ARTICLE  I DEFINITIONS...............................................................................2

         SECTION 1.1.   Certain Defined Terms........................................................2

         SECTION 1.2.   Other Definitional Provisions................................................6

ARTICLE  II CORPORATE GOVERNANCE OF THE COMPANY......................................................6

         SECTION 2.1.   Board Representation.........................................................6

         SECTION 2.2.   Parent Group Covenants.......................................................6

         SECTION 2.3.   Conversion of Class B Common Stock...........................................7

ARTICLE  III REGISTRATION RIGHTS.....................................................................8

         SECTION 3.1.   Registration on Request......................................................8

         SECTION 3.2.   Incidental Registrations....................................................11

ARTICLE  IV REGISTRATION PROCEDURES.................................................................12

         SECTION 4.1.   Registration Procedures.....................................................12

         SECTION 4.2.   Information Supplied........................................................14

         SECTION 4.3.   Restrictions on Disposition.................................................14

         SECTION 4.4.   Indemnification.............................................................15

         SECTION 4.5.   Holdback Agreement..........................................................18

ARTICLE  V MISCELLANEOUS............................................................................18

         SECTION 5.1.   Termination.................................................................18

         SECTION 5.2.   Amendments and Waivers......................................................18

         SECTION 5.3.   Successors, Assigns and Third Party Beneficiaries; No Assignment............18

         SECTION 5.4.   Notices.....................................................................18
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         SECTION 5.5.   Further Assurances..........................................................19

         SECTION 5.6.   Entire Agreement............................................................19

         SECTION 5.7.   Delays or Omissions.........................................................19

         SECTION 5.8.   Governing Law; Jurisdiction; Waiver of Jury Trial...........................20

         SECTION 5.9.   Severability................................................................20

         SECTION 5.10.   Effective Date.............................................................20

         SECTION 5.11.   Enforcement................................................................20

         SECTION 5.12.   Titles and Subtitles.......................................................20

         SECTION 5.13.   Counterparts; Facsimile Signatures.........................................20
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                  STOCKHOLDER AND REGISTRATION RIGHTS AGREEMENT

             THIS STOCKHOLDER AND REGISTRATION RIGHTS AGREEMENT (this
"Agreement") is entered into as of October 6, 2000, between Express Scripts,
Inc., a Delaware corporation (the "Company"), and New York Life Insurance
Company, a New York mutual insurance company ("Parent").

                                    RECITALS

             NYLife Healthcare Management, Inc., a Delaware corporation (the
"Stockholder"), is an indirect, wholly-owned Subsidiary (as defined below) of
Parent.

             The Stockholder is the holder of record of 15,020,000 shares of the
Company's Class B Common Stock, par value $0.01 per share ("Class B Common
Stock"), which are convertible at the option of the holder into an equal number
of shares of the Company's Class A Common Stock, par value $0.01 per share
("Class A Common Stock").

             The Company, at the request of Parent, intends to prepare and file
with the SEC (as defined below) a registration statement relating to the public
offering (the "Stock Offering") of up to 6,900,000 shares of Class A Common
Stock, to be acquired by the Stockholder through the conversion of a like number
of shares of the Class B Common Stock immediately prior to the Closing (as
defined below).

             Parent intends to prepare and file, or cause to be prepared and
filed, with the SEC a registration statement relating to the public offering
(the "Trust Offering") by the Express Scripts Automatic Exchange Security Trust
(the "Trust") of securities which may be exchanged by the Trust for, among other
things, cash or up to 3,450,000 shares of Class A Common Stock (the "Trust
Stock").

             Immediately following the Closing, the Stockholder (or another
member of the Parent Group (as defined below)), in addition to the Trust Stock,
will continue to own shares of Class A Common Stock issued upon the conversion
or exchange of shares of Class B Common Stock (such additional shares issued
upon such conversion or exchange, excluding the Trust Stock, being herein
referred to as the "Retained Stock").

             The parties hereto desire to enter into certain arrangements
relating to the Company, to be effective as of the Closing.

             Accordingly, in consideration of the foregoing recitals and of the
mutual promises hereinafter set forth, the parties hereto agree as follows:
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                                                                               2
                                    ARTICLE I

                                   DEFINITIONS

             SECTION 1.1.  Certain Defined Terms. As used herein, the following
terms shall have the following meanings:

             "Adverse Effect" has the meaning ascribed to such term in Section
3.1(g).

             "Affiliate" means, with respect to any Person, any other Person
that directly or indirectly through one or more intermediaries, controls, is
controlled by or is under common control with, such specified Person, for so
long as such Person remains so associated to the specified Person; provided,
however that for purposes of this Agreement, the Company and its Subsidiaries on
the one hand and Parent and its Affiliates (other than the Company and its
Subsidiaries) on the other hand shall not be deemed to be "Affiliates" of one
another.

             "beneficial owner" or "beneficially own" has the meaning given such
term in Rule 13d-3 under the Exchange Act and a Person's beneficial ownership of
either Common Stock or Preferred Stock or other voting securities of the Company
shall be calculated in accordance with the provisions of such Rule.

             "Board" means the Board of Directors of the Company.

             "Business Day" means any day that is not a Saturday, a Sunday or
other day on which banks are required or authorized by Law to be closed in The
City of New York.

             "Capital Stock" means, with respect to any Person at any time, any
and all shares, interests, participations or other equivalents (however
designated, whether voting or non-voting) of capital stock, partnership
interests (whether general or limited) or equivalent ownership interests in or
issued by such Person and, with respect to the Company, includes any and all
shares of Common Stock and Preferred Stock.

             "Claims" has the meaning assigned to such term in Section 4.4(a).

             "Class A Common Stock" has the meaning assigned to such term in the
recitals.

             "Class B Common Stock" has the meaning assigned to such term in the
recitals.

             "Closing" means either the closing of the Stock Offering or the
Trust Offering.

             "Closing Date" means the date on which the Closing occurs.

             "Common Stock" means the Class A Common Stock and the Class B
Common Stock and any securities issued in respect thereof, or in substitution
therefor, in connection with any stock split, dividend, spin-off or combination,
or any reclassification, recapitalization, merger, consolidation, exchange or
other similar reorganization or business combination.
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                                                                               3

             "Company Offering" has the meaning assigned to such term in Section
3.1(h).

             "control" (including the terms "controlled by" and "under common
control with"), with respect to the relationship between or among two or more
Persons, means the possession, directly or indirectly, of the power to direct or
cause the direction of the affairs or management of a Person, whether through
the ownership of voting securities, as trustee or executor, by contract or
otherwise.

             "Director" means any member of the Board.

             "Equity Securities" means any and all shares of Capital Stock of
the Company, securities of the Company convertible into, or exchangeable or
exercisable for, such shares, and options, warrants or other rights to acquire
such shares.

             "Exchange Act" means the Securities Exchange Act of 1934, as
amended, and the rules and regulations promulgated thereunder.

             "GAAP" means generally accepted accounting principles, as in effect
in the United States of America from time to time.

             "Group" has the meaning assigned to such term in Section 13(d)(3)
of the Exchange Act.

             "Incur" or "Incurrence" means to incur, create, assume, guarantee
or otherwise become directly or indirectly liable with respect to.

             "Indemnified Parties" has the meaning assigned to such term in
Section 4.4(a).

             "Investment Subsidiaries" means (i) Subsidiaries of Parent engaged
in the ownership and/or management of assets (a) held by Parent in a fiduciary
or custodial capacity or (b) of third parties and (ii) Parent, but only with
respect to, and to the extent it, alone or together with sub-advisors, manages
assets of third parties.

             "Law" means any statute, law, ordinance, regulation, rule, code,
order or other requirement or rule of law.

             "NASD" means the National Association of Securities Dealers, Inc.

             "NASDAQ" means The Nasdaq Stock Market.

             "Parent Group" means Parent and each of its Subsidiaries (including
the Stockholder but excluding the Investment Subsidiaries and the Company); if
at any time any Person (including the Stockholder) ceases to be a Subsidiary of
Parent, it shall simultaneously cease to be (i) a member of the Parent Group for
purposes of this Agreement and (ii) entitled to the benefits conferred upon
members of the Parent Group hereunder.

             "Parent Representatives" has the meaning assigned to such term in
Section 2.1(a).
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                                                                               4

             "Person" means any individual, corporation, limited liability
company, limited or general partnership, joint venture, association, joint-stock
company, trust, unincorporated organization, government or any agency or
political subdivisions thereof or any Group comprised of two or more of the
foregoing.

             "Preferred Stock" means the Company's preferred stock, par value
$0.01 per share.

             "Registrable Securities" means the Retained Stock and (i) any
additional Capital Stock of the Company issued in substitution therefor, or in
respect thereof, pursuant to any stock split, dividend, spin-off, combination,
or any reclassification by the Company and (ii) any Capital Stock issued in
substitution therefor, or in respect thereof, in connection with any
recapitalization, merger, consolidation, exchange or other similar
reorganization or business combination; provided that, with respect to the
Capital Stock referred to in clause (ii), Parent or a member of the Parent Group
is otherwise unable to sell such Capital Stock on a U.S. national securities
exchange or over-the-counter market in a manner similar to that which would be
permitted under Rule 144 of the Securities Act if paragraphs (c), (e), (f) and
(h) of such rule did not apply. As to any particular Registrable Securities,
such Registrable Securities shall cease to be Registrable Securities when (a)
such securities cease to be held by a member of the Parent Group, (b) a
registration statement with respect to the sale by any member of the Parent
Group of such securities shall have become effective under the Securities Act
and such securities shall have been disposed of in accordance with such
registration statement, (c) such securities shall have been distributed to the
public pursuant to Rule 144 or (d) such securities shall have ceased to be
outstanding.

             "Registration Expenses" means the following expenses incident to
performance of or compliance with Articles III and IV: (i) all SEC and any
securities exchange, NASD or NASDAQ registration and filing fees; (ii) all fees
and expenses of complying with securities or blue sky laws (including the
reasonable fees and disbursements of counsel for the underwriters in connection
with blue sky qualifications of the Registrable Securities); (iii) all printing,
messenger and delivery expenses; (iv) all fees and expenses incurred in
connection with any required listing of the Registrable Securities on any
securities exchange or NASDAQ; (v) the fees and disbursements of counsel for the
Company and of its independent public accountants, including the expenses of any
special audits, "cold comfort" letters and/or legal opinions of Company counsel
required by or incident to such performance and compliance; (vi) any reasonable
fees and disbursements of special experts retained in connection with the
requested registration, but excluding the fees and disbursements of any counsel
for any member of the Parent Group or the Investment Subsidiaries, underwriting
discounts and commissions and transfer taxes, if any; and (vii) all expenses
reasonably incurred in connection with road shows.

             "Retained Stock" has the meaning assigned to such term in the
recitals, plus (from and after the date of the termination of the Trust) the
shares of Trust Stock in excess of the number of shares of Trust Stock necessary
to settle the Parent Group's delivery obligations pursuant to the purchase
agreement entered into in connection with the Trust Offering (whether or not the
Trust Stock is used to settle such obligations); provided that any such excess
shares of Trust Stock are released from the collateral arrangements entered into
by Parent or any other member of the Parent Group in connection with the Trust
Offering. References herein to
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numbers of shares of Retained Stock shall be appropriately adjusted to give
effect to any stock split, reverse stock split, stock dividend or similar
recapitalization event, and any merger, consolidation, exchange or other similar
reorganization or business combination involving the Company, occurring after
the Closing.

             "Rule 144" means Rule 144 (or any successor provision) under the
Securities Act.

             "SEC" means the U.S. Securities and Exchange Commission or any
other federal agency then administering the Securities Act or the Exchange Act
and other federal securities laws.

             "Securities Act" means the Securities Act of 1933, as amended, and
the rules and regulations promulgated thereunder.

             "Shelf Registration" has the meaning assigned to such term in
Section 3.1(b).

             "Stock Offering" has the meaning assigned to such term in the
recitals.

             "Stockholder" has the meaning assigned to such term in the
recitals.

             "Subsidiary" means (i) any corporation of which a majority of the
securities entitled to vote generally in the election of directors thereof, at
the time as of which any determination is being made, are owned by another
entity, either directly or indirectly, and (ii) any joint venture, general or
limited partnership, limited liability company or other legal entity in which an
entity is the record or beneficial owner, directly or indirectly, of a majority
of the voting interests or the general partner.

             "Transaction Delay Notice" has the meaning assigned to such term in
Section 3.1(h).

             "Transfer" means, directly or indirectly, to sell, transfer,
assign, pledge, encumber, hypothecate or similarly dispose of, either
voluntarily or involuntarily, or to enter into any contract, option or other
arrangement or understanding with respect to the sale, transfer, assignment,
pledge, encumbrance, hypothecation or similar disposition of, any shares of
Equity Securities beneficially owned by a Person or any interest in any shares
of Equity Securities beneficially owned by a Person.

             "Trust" has the meaning assigned to such term in the recitals.

             "Trust Offering" has the meaning assigned to such term in the
recitals.

             "Trust Stock" has the meaning assigned to such term in the
recitals.

             "Underwritten Registration" has the meaning assigned to such term
in Section 3.1(b).

             "Voting Securities" means, at any time, shares of any class of
Equity Securities that are then entitled to vote generally in the election of
Directors.
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             SECTION 1.2.  Other Definitional Provisions. (a) The words
"hereof," "herein" and "hereunder" and words of similar import when used in this
Agreement shall refer to this Agreement as a whole and not to any particular
provision of this Agreement, and Article and Section references are to this
Agreement unless otherwise specified.

             (b) The meanings given to terms defined herein shall be equally
applicable to both the singular and plural forms of such terms.

                                   ARTICLE II

                      CORPORATE GOVERNANCE OF THE COMPANY

             SECTION 2.1. Board Representation. (a) Parent shall be entitled to
designate two people (the "Parent Representatives") for election to the Board,
and the Company agrees, to the extent permitted by Law, to take such action as
may be required under applicable Law (i) so that, effective as of the Closing,
the Board shall include the Parent Representatives, (ii) to include the Parent
Representatives in any slate of nominees for Directors recommended by the Board
for election by the stockholders of the Company and (iii) to use the same
efforts to cause the election of the Parent Representatives to the Board as the
Company uses with respect to the Company's other nominees for Directors,
including nominating such individuals to be elected as Directors; provided that
such Parent Representatives must be either (A) senior executive officers of
Parent at the time of their designation hereunder or (B) other people reasonably
satisfactory to the Company at the time of their designation hereunder; and
provided further that if all of the members of the Parent Group, in the
aggregate, own at least 1.5 million shares of Retained Stock and such ownership
interest represents less than 5% of the total voting power of the Company's
outstanding Voting Securities, the number of Parent Representatives shall be
reduced to one, and if all of the members of the Parent Group, in the aggregate,
own less than 1.5 million shares of Retained Stock the number of Parent
Representatives shall be reduced to zero. Parent shall cause each of its
designees to the Board, other than the initial Parent Representatives, to resign
from the Board effective as of the Closing.

             (b) In the event that a vacancy is created on the Board at any time
by the death, disability, retirement, resignation or removal (with or without
cause) of a Parent Representative, the Company shall use its best efforts to
cause the remaining Directors to cause the vacancy created thereby to be filled
by a new designee of Parent in accordance with the terms of Section 2.1, and the
Company hereby agrees to take, or cause to be taken, at any time and from time
to time, all actions necessary to accomplish the same. The Company shall not
take any action to cause the removal of a Parent Representative, by stockholders
of the Company, without cause, or otherwise.

             (c) As long as Parent is entitled to two Parent Representatives
pursuant to the terms of Section 2.1(a), each standing committee of the Board
(other than the audit committee) shall include one of the Parent
Representatives.

             SECTION 2.2.  Parent Group Covenants. (a) To the extent that
approval of the stockholders of the Company is required by Law or by its
certificate of incorporation or by-laws,
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                                                                               7

Parent shall and shall cause each other member of the Parent Group to (i) vote
any shares of Voting Securities held by it (including the Retained Stock and
Trust Stock) in favor of the slate of nominees for Directors recommended by the
Board for election by the stockholders of the Company; provided that, so long as
Parent is entitled to Parent Representative(s) pursuant to the terms of Section
2.1(a), such slate includes the Parent Representative(s) to which Parent is
entitled; (ii) vote any shares of Voting Securities held by it (including the
Retained Stock and Trust Stock) to approve the Express Scripts, Inc. 2000
Long-Term Incentive Plan, as approved by the Board, when submitted for the
approval of the stockholders of the Company; and (iii) except as provided in the
preceding clause (ii), vote any shares of Trust Stock held by it, at any regular
or special meeting of the stockholders of the Company or in any written consent
executed in lieu of such a meeting of stockholders, in the same proportion and
to the same effect as the votes cast by other stockholders of the Company.

             (b) For the avoidance of doubt, except as set forth in Section
2.2(a), and except as would conflict with the provisions of this Agreement, the
applicable members of the Parent Group shall be entitled to vote the Retained
Stock in their sole discretion.

             (c) To effectuate the provisions of Sections 2.2(a) and (b), the
Secretary of the Company, or if there be no Secretary, such other officer of the
Company as the Board may appoint to fulfill the duties of Secretary, shall not
record any vote or consent contrary to the terms of Section 2.2(a) or (b).

             (d) During the 90 day period following the Closing Date, subject to
the exceptions provided in the underwriting agreement relating to the Stock
Offering but regardless of any waiver thereunder, Parent agrees not to, and
agrees to cause each other member of the Parent Group not to, effect any
Transfer of, or grant any rights to, any Person (other than a member of the
Parent Group) relating to any Equity Securities held by any member of the Parent
Group (including any sale pursuant to Rule 144 under the Securities Act) other
than as contemplated by the Trust Offering and the Stock Offering.

             SECTION 2.3.  Conversion of Class B Common Stock. This Agreement
shall constitute Parent's irrevocable direction to the Company (for itself and
on behalf of the Stockholder and any other member of the Parent Group and the
Investment Subsidiaries), effective at the time of the Closing, to convert each
issued and outstanding share of Class B Common Stock not theretofore converted
into Class A Common Stock into one fully paid and nonassessable share of Class A
Common Stock. If neither Closing occurs, this direction shall be null and void.
Upon such conversion, Class B Common Stock certificates shall represent only the
right to receive, upon surrender thereof, a certificate representing an
identical number of shares of Class A Common Stock and Parent shall surrender
all such Class B Common Stock certificates in exchange for certificates
representing the shares of Class A Common Stock issued upon such conversion.
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                                                                               8

                                  ARTICLE III

                              REGISTRATION RIGHTS

             SECTION 3.1.  Registration on Request.

             (a) Request. Subject to the further provisions of this Agreement,
so long as all of the members of the Parent Group, in the aggregate, hold in
excess of 1.5 million shares of Retained Stock, Parent may request in writing
that the Company effect the registration under the Securities Act of all or part
of the Registrable Securities. Any such request will specify (i) the number of
Registrable Securities proposed to be sold and (ii) subject to the other
provisions of this Section 3.1, the intended method of disposition thereof.
Subject to the other provisions of this Section 3.1, the Company shall use its
reasonable best efforts to effect the registration under the Securities Act of
the Registrable Securities that the Company has been so requested to register by
Parent.

             (b) Limits on Registration Requests. Notwithstanding Section
3.1(a), (i) in no event shall the Company be required to effect more than three
registrations pursuant to Section 3.1(a), one of which may be requested to be
effected as a shelf registration pursuant to Rule 415 under the Securities Act
(such registration request, a "Shelf Registration") and two of which may be
requested to be effected as firm commitment underwritten offerings under and in
accordance with the provisions of the Securities Act (each such registration
request, an "Underwritten Registration"), and (ii) the Company shall not be
obligated to file a registration statement relating to any registration request
under Section 3.1(a) (A) within a period of 90 days after the effective date of
any other registration statement of the Company (other than a registration
statement on Form S-8 or any successor or other form hereafter promulgated for
similar purposes), except to the extent that the deferral would result in a
filing date that is more than 120 days after Parent first requested such
registration in accordance with Section 3.1(a), (B) within a period of 180 days
after the Closing Date or (C) while a registration statement relating to a Shelf
Registration is effective under the Securities Act.

             (c) Registration Statement Form. The Company shall select the
registration statement form for any registration pursuant to Section 3.1(a);
provided that the prospectus included in the registration statement for an
Underwritten Registration shall include such information required by Form S-1
(or any successor form) as the managing underwriters may reasonably request.

             (d) Expenses. The Company will pay all Registration Expenses in
connection with registrations pursuant to Section 3.1(a).

             (e) Effective Registration Statement. A registration requested
pursuant to Section 3.1(a) will not be deemed to have been effected:

             (i) unless a registration statement with respect thereto has become
effective and remained effective in compliance with the provisions of the
Securities Act with respect to the disposition of all Registrable Securities
covered by such registration statement
<PAGE>   12
                                                                               9

until the earlier of (A) such time as all of such Registrable Securities have
been disposed of in accordance with the intended methods of disposition thereof
set forth in such registration statement or (B) 18 months after the effective
date of such registration statement, in the case of a Shelf Registration and 90
days after the effective date of such registration statement, in the case of
Underwritten Registrations (in either case, as such periods may be extended
pursuant to the terms of this Agreement); provided, that if the failure of any
such registration statement to become or remain effective in compliance with
this Section 3.1(e)(i) is due solely to the failure of a member of the Parent
Group to comply with its obligations under this Agreement or any applicable
underwriting agreement, such registration requested pursuant to Section 3.1(a)
will be deemed to have been effected;

             (ii) if after it has become effective, the registration statement
is interfered with by any stop order, injunction or other order or requirement
of the SEC or other governmental agency or authority and does not thereafter
become effective and remain effective for an aggregate period equal to the
period specified in clause (i); or

             (iii) if the conditions to closing specified in the underwriting
agreement, if any, entered into in connection with such registration are not
satisfied or waived, other than by reason of a failure on the part of a member
of the Parent Group to comply with its obligations hereunder or under any
applicable underwriting agreement.

             (f) Underwritten Offering. The investment banker(s), underwriter(s)
and manager(s) for Underwritten Registrations shall be selected by Parent;
provided, however, that such investment banker(s), underwriter(s) and manager(s)
shall be reasonably satisfactory to the Company.

             (g) Priority in Requested Registrations. If the managing
underwriter in an Underwritten Registration advises the Company in writing that,
in its opinion, the number of any securities proposed to be included in such
registration for issuance and sale by the Company would be likely to have an
adverse effect on the price, timing or distribution of the securities to be
offered in such offering as contemplated by Parent (an "Adverse Effect"), then
the Company shall include securities in such registration by Parent only to the
extent that the managing underwriter believes that such Registrable Securities
can be sold in such offering without having an Adverse Effect. No securities
held by any other stockholder shall be included in any Underwritten
Registration. If the managing underwriter of an Underwritten Registration shall
advise Parent that the Registrable Securities covered by the registration
statement cannot be sold in such offering within a price range acceptable to
Parent, then Parent shall have the right to notify the Company that it has
determined that the registration statement be abandoned or withdrawn, in which
event the Company shall abandon or withdraw such registration statement.

             (h) Postponements in Requested Registrations. (i) If, upon receipt
of a registration request pursuant to Section 3.1(a), the Company is advised in
writing by a nationally recognized investment banking firm selected by the
Company that, in such firm's opinion, a registration at the time and on the
terms requested would materially and adversely affect any public offering of
securities of the Company by the Company (other than in connection with employee
benefit and similar plans) (a "Company Offering") with respect to which the
Company has commenced preparation of a registration statement prior to the
receipt of a registration
<PAGE>   13
                                                                              10

request pursuant to Section 3.1(a) and the Company furnishes Parent with a
certificate signed by the Chief Executive Officer or Chief Financial Officer of
the Company to such effect (the "Transaction Delay Notice") promptly after such
request, the Company shall not be required to effect a registration pursuant to
Section 3.1(a) until the earliest of (A) 60 days after the completion of such
Company Offering, (B) promptly after the abandonment of such Company Offering or
(C) 180 days after the date of the Transaction Delay Notice; provided, however,
that in any event the Company shall not be required to effect any registration
prior to the termination, waiver or reduction of any "blackout" or "holdback"
period required by Section 2.2(d) or 4.5, if any, in connection with any Company
Offering.

             (ii) If upon receipt of a registration request pursuant to Section
3.1(a) or while a registration request pursuant to Section 3.1(a) is pending,
the Company determines in its reasonable judgment after consultation with its
securities counsel that the filing of a registration statement would require
disclosure of material information which the Company has a bona fide business
purpose for preserving as confidential and the Company provides Parent written
notice thereof promptly after the Company makes such determination, which shall
be made promptly after the receipt of any request, the Company shall not be
required to comply with its obligations under Section 3.1(a) until the earlier
of (A) the date upon which such material information is disclosed to the public
or ceases to be material or (B) 120 days after the Parent's receipt of such
notice.

             (iii) At any time when a registration statement effected pursuant
to Section 3.1(a) relating to a Shelf Registration is effective and a prospectus
relating thereto is required to be delivered under the Securities Act within the
appropriate period mentioned in Section 4.1(a), that the Company becomes aware
that the prospectus included in such registration statement, as then in effect,
includes an untrue statement of a material fact or omits to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading in the light of the circumstances then existing, then, to the
extent that the amendment or supplement to such prospectus necessary to correct
such untrue statement of a material fact or omission to state a material fact
would require disclosure of material information which the Company has a bona
fide business purpose for preserving as confidential and the Company provides
Parent written notice thereof promptly after the Company makes such
determination, Parent shall, and shall cause each other member of the Parent
Group to, suspend sales of Registrable Securities pursuant to such registration
statement and the Company shall not be required to comply with its obligations
under Section 4.1(f) until the earlier of (A) the date upon which such material
information is disclosed to the public or ceases to be material or (B) 120 days
after Parent's receipt of such written notice. If the disposition of Registrable
Securities by any member of the Parent Group in an Underwritten Registration is
discontinued pursuant to the foregoing sentence, unless the Company thereafter
extends the effectiveness of the registration statement relating to such
Underwritten Registration to permit dispositions of Registrable Securities by
the applicable members of the Parent Group for an aggregate of at least 60 days,
such registration statement shall not be counted for purposes of determining the
number of registrations permitted under Section 3.1(b).

             (iv) Notwithstanding the provisions of Section 3.1(b)(ii)(A) and
this Section 3.1(h), the Company may not defer the filing of, or suspend the use
of, any registration statement contemplated by Section 3.1 for more than 120
days (whether or not consecutive) in
<PAGE>   14
                                                                              11

any 365-day period (except as explicitly contemplated by clauses (B) and (C) of
Section 3.1(b)(ii)).

             SECTION 3.2.  Incidental Registrations. (a) If the Company, at
any time after the Closing, proposes to register Common Stock under the
Securities Act (other than a registration on Form S-4 or S-8, or any successor
or other forms promulgated for similar purposes), for sale for its own account,
in a manner which would permit registration of Registrable Securities for sale
to the public under the Securities Act and all of the members of the Parent
Group, in the aggregate, hold in excess of 1.5 million shares of Retained Stock,
it will, at each such time, give prompt written notice to Parent of its
intention to do so and of Parent's rights under this Agreement. Upon the written
request of Parent made within 30 days after the receipt of any such notice
(which request shall specify the Registrable Securities intended to be disposed
of by the Parent Group), the Company will use its reasonable best efforts to
effect the registration under the Securities Act of all Registrable Securities
which the Company has been so requested to register by Parent; provided, that
(i) if, at any time after giving written notice of its intention to register any
securities and prior to the effective date of the registration statement filed
in connection with such registration, the Company shall determine for any reason
not to proceed with the proposed registration of the securities to be sold by
it, the Company may, at its election, give written notice of such determination
to Parent and, thereupon, shall be relieved of its obligation to register any
Registrable Securities in connection with such registration (but not from its
obligation to pay the Registration Expenses in connection therewith), and (ii)
if such registration involves an underwritten offering, if Parent requests to be
included in the Company's registration the applicable members of the Parent
Group must sell their Registrable Securities to the underwriters selected by the
Company (if they sell such securities pursuant to such registration statement)
on the same terms and conditions as apply to the Company, with such differences,
including any with respect to indemnification and liability insurance, as may be
customary or appropriate in combined primary and secondary offerings. If a
registration requested pursuant to this Section involves an underwritten public
offering, Parent may elect, in writing prior to the effective date of the
registration statement filed in connection with such registration, not to
register all or any part of such securities in connection with such
registration. The registrations provided for in this Section 3.2 are in addition
to, and not in lieu of, registrations made upon the request of Parent in
accordance with Section 3.1.

             (b) Expenses. The Company will pay all Registration Expenses in
connection with each registration of Registrable Securities requested pursuant
to Section 3.2(a).

             (c) Priority in Incidental Registrations. If a registration
pursuant to Section 3.2(a) involves an underwritten offering and the managing
underwriter advises the Company in writing that, in its opinion, the number of
Registrable Securities requested to be included in such registration by the
Parent Group would be likely to have an Adverse Effect (other than with respect
to the Registrable Securities), then the Company shall include in such
registration (a) first, 100% of the securities the Company proposes to sell and
(b) second, to the extent of the amount of Registrable Securities requested to
be included in such registration, the amount thereof that, in the opinion of
such managing underwriter, can be sold without having the Adverse Effect
referred to above.
<PAGE>   15
                                                                              12

                                   ARTICLE IV

                             REGISTRATION PROCEDURES

             SECTION 4.1.  Registration Procedures. If and whenever the Company
is required to use its reasonable best efforts to effect or cause the
registration of any Registrable Securities under the Securities Act as provided
in this Agreement, the Company will, as expeditiously as possible:

             (a) prepare and, in any event within 45 days after a request for
registration is given to the Company file with the SEC a registration statement
with respect to such Registrable Securities and use its reasonable best efforts
to cause such registration statement to become effective as soon as practicable
and in any event within 90 days of the initial filing; provided, that before
filing a registration statement, or any amendments or supplements thereto in
accordance with Section 4.1(b), the Company will furnish to one counsel selected
by the sellers of a majority of the Registrable Securities covered by such
registration statement to represent all sellers of Registrable Securities
covered by such registration statement, copies of all documents proposed to be
filed, which documents will be subject to the review and comment of such
counsel;

             (b) prepare and file with the SEC such amendments and supplements
to such registration statement and the prospectus used in connection therewith
as may be necessary to keep such registration statement effective for a period
not in excess of 18 months in the case of a Shelf Registration and 90 days in
the case of any other registration (in either case, as such periods may be
extended pursuant to the terms of this Agreement), and to comply with the
provisions of the Securities Act and the Exchange Act with respect to the
disposition of all securities covered by such registration statement during such
period in accordance with the intended methods of disposition by the seller or
sellers thereof set forth in such registration statement;

             (c) furnish to each seller of such Registrable Securities such
number of copies of such registration statement and of each amendment and
supplement thereto (in each case including all exhibits filed therewith,
including any documents incorporated by reference), such number of copies of the
prospectus included in such registration statement (including each preliminary
prospectus and summary prospectus), in conformity with the requirements of the
Securities Act, and such other documents as such seller may reasonably request
in order to facilitate the disposition of the Registrable Securities by such
seller;

             (d) use its reasonable best efforts to register or qualify such
Registrable Securities covered by such registration in such jurisdictions as
each seller shall reasonably request, and do any and all other acts and things
which may be reasonably necessary or advisable to enable such seller to
consummate the disposition in such jurisdictions of the Registrable Securities
owned by such seller, except that the Company shall not for any such purpose be
required to qualify generally to do business as a foreign corporation in any
jurisdiction where, but for the requirements of this subsection (d), it would
not be obligated to be so qualified, to
<PAGE>   16
                                                                              13

subject itself to taxation in any such jurisdiction or to consent to general
service of process in any such jurisdiction;

             (e) use its reasonable best efforts to cause such Registrable
Securities covered by such registration statement to be registered with or
approved by such other governmental authorities as may be necessary to enable
the seller or sellers thereof to consummate the disposition of such Registrable
Securities; provided that any such registration or approval required solely
because of the regulatory status of any member of the Parent Group shall be at
Parent's expense;

             (f) notify each seller of any such Registrable Securities covered
by such registration statement, at any time when a prospectus relating thereto
is required to be delivered under the Securities Act, of the Company's becoming
aware that the prospectus included in such registration statement, as then in
effect, includes an untrue statement of a material fact or omits to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading in the light of the circumstances then existing, and at
the request of any such seller (except to the extent otherwise permitted by the
terms of this Agreement), prepare and furnish to such seller a reasonable number
of copies of an amended or supplemental prospectus as may be necessary so that,
as thereafter delivered to the sellers of such Registrable Securities, such
prospectus shall not include an untrue statement of a material fact or omit to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing;

             (g) enter into such customary agreements (including an underwriting
agreement in customary form), which may include indemnification and contribution
provisions in favor of underwriters and other Persons in addition to, or in
substitution for the provisions of Section 4.4, perform its obligations
thereunder and use its reasonable best efforts to cause the conditions to the
underwriters' obligations thereunder to be satisfied;

             (h) use its reasonable best efforts to obtain a "cold comfort"
letter or letters from the Company's independent public accountants and legal
opinions from its counsel in customary form and covering matters of the type
customarily covered by "cold comfort" letters and legal opinions as the seller
or sellers of a majority of shares of such Registrable Securities shall
reasonably request;

             (i) notify the sellers of Registrable Securities included in such
registration statement and the managing underwriter or agent, immediately, and
confirm the notice in writing (i) when the registration statement, or any
post-effective amendment to the registration statement, shall have become
effective, or any supplement to the prospectus or any amendment to the
prospectus shall have been filed, (ii) of the receipt of any comments from the
SEC, (iii) of any request of the SEC to amend the registration statement or
amend or supplement the prospectus or for additional information, and (iv) of
the issuance by the SEC of any stop order suspending the effectiveness of the
registration statement or of any order preventing or suspending the use of any
preliminary prospectus, or of the suspension of the qualification of the
registration statement for offering or sale in any jurisdiction, or of the
institution or threatening of any proceedings for any of such purposes;
<PAGE>   17
                                                                              14

             (j) use its reasonable best efforts to prevent the issuance of any
stop order suspending the effectiveness of the registration statement or of any
order preventing or suspending the use of any preliminary prospectus and, if any
such order is issued, to obtain the withdrawal of any such order at the earliest
possible moment;

             (k) cooperate with the sellers of Registrable Securities covered by
the registration statement and the managing underwriter or agent, if any, to
facilitate the timely preparation and delivery of certificates (not bearing any
restrictive legends) representing securities to be sold under the registration
statement, and enable such securities to be in such denominations and registered
in such names as the managing underwriter or agent, if any, or such sellers may
request;

             (l) cooperate with each seller of Registrable Securities and each
underwriter or agent participating in the disposition of such Registrable
Securities and their respective counsel in connection with any filings required
to be made with any securities exchange and/or the NASDAQ;

             (m) make available for inspection by representatives of the sellers
of Registrable Securities covered by such registration statement, by any
underwriter participating in any disposition to be effected pursuant to such
registration statement and by any attorney, accountant or other agent retained
by such sellers or any such underwriter, all pertinent financial and other
records, pertinent corporate documents and properties of the Company, and cause
all of the Company's officers, directors and employees to supply all information
reasonably requested in accordance with customary practice by any such seller,
underwriter, attorney, accountant or agent in connection with such registration
statement (subject to each party referred to in this clause (m) entering into
customary confidentiality agreements in a form reasonably acceptable to the
Company); and

             (n) make available the senior executive officers of the Company to
participate in customary "road show" presentations that may be reasonably
requested by the managing underwriter in any Underwritten Offering; provided
that the participation of such senior executive officers shall not unreasonably
interfere with the Company's business.

             SECTION 4.2. Information Supplied. The Company may require each
seller of Registrable Securities as to which any registration is being effected
to furnish information regarding such seller and pertinent to the disclosure
requirements relating to the registration and the distribution of such
securities as the Company may from time to time reasonably request in writing.

             SECTION 4.3. Restrictions on Disposition. Parent agrees that, upon
receipt of any notice from the Company of the happening of any event of the kind
described in Section 4.1(f), Parent shall, and shall cause each other member of
the Parent Group to, forthwith discontinue disposition of Registrable Securities
pursuant to the registration statement covering such Registrable Securities
until Parent's receipt of the copies of the supplemented or amended prospectus
contemplated by Section 4.1(f), and, if so directed by the Company, Parent
shall, and shall cause each other member of the Parent Group to, deliver to the
Company (at the Company's expense) all copies, other than permanent file copies,
then in Parent's or such other
<PAGE>   18
                                                                              15

member's possession of the prospectus covering such Registrable Securities
current at the time of receipt of such notice. In the event the Company shall
give any such notice, the period mentioned in Section 4.1(b) shall be extended
by the number of days during the period from and including the date of the
giving of such notice pursuant to Section 4.1(f) and to and including the date
when each seller of Registrable Securities covered by such registration
statement shall have received the copies of the supplemented or amended
prospectus contemplated by Section 4.1(f) or, if the managing underwriter of an
Underwritten Offering reasonably concludes that it would be impractical to
complete such offering as a result of the occurrence of such event, such
registration may be abandoned and deemed not to have been effected or requested.

             SECTION 4.4. Indemnification. (a) In the event of any registration
of any securities of the Company under the Securities Act pursuant to Article
III, the Company shall, and it hereby agrees to, indemnify and hold harmless, to
the extent permitted by Law, the seller of any Registrable Securities covered by
such registration statement, each Affiliate of such seller and their respective
directors, officers, employees and stockholders or members or general and
limited partners (and any director, officer, Affiliate, employee, stockholder
and controlling Person of any of the foregoing), each Person who participates as
an underwriter in the offering or sale of such securities and each other Person,
if any, who controls such seller or any such underwriter within the meaning of
the Securities Act or the Exchange Act (collectively, the "Indemnified
Parties"), against any and all losses, claims, damages or liabilities, joint or
several, actions or proceedings (whether commenced or threatened) in respect
thereof ("Claims") and expenses (including reasonable attorney's fees and
reasonable expenses of investigation) to which such Indemnified Party may become
subject under the Securities Act or the Exchange Act, common Law or otherwise,
insofar as such Claims or expenses arise out of, relate to or are based upon (i)
any untrue statement or alleged untrue statement of any material fact contained
in any registration statement under which such securities were registered under
the Securities Act, any preliminary, final or summary prospectus contained
therein, or any amendment or supplement thereto, or (ii) any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein (in the case of a prospectus, in light
of the circumstances under which they were made) not misleading; provided, that
the Company shall not be liable to any Indemnified Party in any such case to the
extent that any such Claim or expense arises out of, relates to or is based upon
any untrue statement or alleged untrue statement or omission or alleged omission
made in such registration statement or amendment or supplement thereto or in any
such preliminary, final or summary prospectus in reliance upon and in conformity
with information furnished by any Indemnified Party to the Company in writing
expressly for use therein; and, provided, further, that the Company will not be
liable to any Indemnified Party (or any Person controlling such Indemnified
Party) who is obligated to deliver a prospectus in transactions in a security as
to which a registration statement has been filed pursuant to the Securities Act
and from whom the Person asserting any such Claims purchased any of the
Registrable Securities to the extent that it is finally judicially determined by
a court of competent jurisdiction from which an appeal cannot be taken that such
Claims resulted solely from the fact that such party sold Registrable Securities
to a Person to whom there was not sent or given, at or prior to the written
confirmation of such sale, a copy of the registration statement or the
prospectus, as amended or supplemented, and (A) the Company shall have
previously and timely furnished sufficient copies of the registration statement
or prospectus, as so amended or supplemented, to such party in accordance with
this Agreement and (B) the registration statement or prospectus, as so amended
or supplemented, corrected such
<PAGE>   19
                                                                              16

untrue statement or omission of a material fact. Such indemnity shall remain in
full force and effect regardless of any investigation made by or on behalf of
any Indemnified Party and shall survive the transfer of securities by any
seller.

             (b) The Company may require, as a condition to including any
Registrable Securities in any registration statement filed in accordance with
Section 3.1 or 3.2 that it shall have received an undertaking reasonably
satisfactory to it from Parent and other applicable members of the Parent Group
to indemnify and hold harmless (in the same manner and to the same extent as set
forth in Section 4.4(a)) the Company or any underwriter, as the case may be,
with respect to any untrue statement or alleged untrue statement in or omission
or alleged omission from such registration statement, any preliminary, final or
summary prospectus contained therein, or any amendment or supplement thereto, if
such untrue statement or alleged untrue statement or omission or alleged
omission was made in reliance upon and in conformity with information furnished
by any Indemnified Party to the Company in writing expressly for use therein.
Such indemnity shall remain in full force and effect regardless of any
investigation made by or on behalf of the Company or any of the prospective
sellers, or any of their respective Affiliates, directors, officers or
controlling Persons and shall survive the transfer of securities by any seller.

             (c) The Company may require, as a condition to including any
Registrable Securities in any registration statement filed in accordance with
Section 3.1 or 3.2, that any underwriter participating in any disposition to be
effected pursuant to any such registration statement shall have entered into
agreements including customary indemnification and contribution provisions in
favor of the Company.

             (d) Promptly after receipt by an indemnified party hereunder of
written notice of the commencement of any action or proceeding with respect to
which a claim for indemnification may be made pursuant to this Section 4.4, such
indemnified party will, if a claim in respect thereof is to be made against an
indemnifying party, give written notice to the latter of the commencement of
such action or proceeding; provided, however, that the failure of the
indemnified party to give notice as provided herein shall not relieve the
indemnifying party of its obligations under Section 4.4, except to the extent
that the indemnifying party is materially prejudiced by such failure to give
notice. In case any such action or proceeding is brought against an indemnified
party, unless in such indemnified party's reasonable judgment (after
consultation with legal counsel) a conflict of interest between such indemnified
and indemnifying parties may exist in respect of such action or proceeding or
the indemnified party has one or more potential defenses not available to the
indemnifying party (in either case, the indemnifying party shall not have the
right to assume the defense of such action on behalf of the indemnified party
and the indemnifying party shall pay the reasonable expenses of counsel for the
indemnified party in connection with such defense), the indemnifying party will
be entitled to participate in and to assume the defense thereof (at its
expense), jointly with any other indemnifying party similarly notified to the
extent that it may wish, with counsel reasonably satisfactory to such
indemnified party, and after notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof, the
indemnifying party will not be liable to such indemnified party for any legal or
other expenses subsequently incurred by the latter in connection with the
defense thereof other than reasonable costs of investigation; provided that, in
the event, however, that the indemnifying party declines or fails to assume the
<PAGE>   20
                                                                              17

defense of the action or proceeding or to employ counsel reasonably satisfactory
to the indemnified party, in either case within a 30-day period, or if the
indemnifying party is not vigorously defending such action or proceeding, then
such indemnified party may employ counsel to represent or defend it in any such
action or proceeding and the indemnifying party shall pay the reasonable fees
and disbursements of such counsel or other representative as incurred; provided,
however, that the indemnifying party shall not be required to pay the fees and
disbursements of more than one counsel for all indemnified parties (any one
additional counsel for underwriters) in any single jurisdiction in any single
action or proceeding. No indemnifying party will settle any such action or
proceeding or consent to the entry of any judgment without the prior written
consent of the indemnified party, unless such settlement or judgment (i)
includes as an unconditional term thereof the giving by the claimant or
plaintiff of a release to such indemnified party from all liability in respect
of such action or proceeding and (ii) does not involve the imposition of
equitable remedies or the imposition of any obligations on such indemnified
party and does not otherwise adversely affect such indemnified party, other than
as a result of the imposition of financial obligations for which such
indemnified party will be indemnified hereunder. No indemnified party will
settle any such action or proceeding or consent to the entry of any judgment
without the prior written consent of the indemnifying party (such consent not to
be unreasonably withheld).

             (e) (i) If the indemnification provided for in this Section 4.4
from the indemnifying party is unavailable to an indemnified party hereunder in
respect of any Claim or expenses referred to herein, then the indemnifying
party, in lieu of indemnifying such indemnified party, shall contribute to the
amount paid or payable by such indemnified party as a result of such Claim or
expenses in such proportion as is appropriate to reflect the relative fault of
the indemnifying party and indemnified party in connection with the actions,
statements or omissions which resulted in such Claim or expenses, as well as any
other relevant equitable considerations. The relative fault of such indemnifying
party and indemnified party shall be determined by reference to, among other
things, whether any action in question, including any untrue or alleged untrue
statement of a material fact or omission or alleged omission to state a material
fact, has been made by, or relates to information supplied by, such indemnifying
party or indemnified party, and the parties' relative intent, knowledge, access
to information and opportunity to correct or prevent such action, statement or
omission. The amount paid or payable by a party under this Section 4.4(e) as a
result of the Claim and expenses referred to above shall be deemed to include
any legal or other fees or expenses reasonably incurred by such party in
connection with any action or proceeding.

             (ii) The parties hereto agree that it would not be just and
equitable if contribution pursuant to this Section 4.4(e) were determined by pro
rata allocation or by any other method of allocation which does not take account
of the equitable considerations referred to in Section 4.4(e)(i). No Person
guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of
the Securities Act) shall be entitled to contribution from any Person who was
not guilty of such fraudulent misrepresentation.

             (f) Indemnification similar to that specified in this Section 4.4
(with appropriate modifications) shall be given by the Company and each seller
of Registrable Securities with respect to any required registration or other
qualification of securities under any Law or with any governmental authority
other than as required by the Securities Act.
<PAGE>   21
                                                                              18

             (g) The obligations of the parties under this Section 4.4 shall be
in addition to any liability which any party may otherwise have to any other
party.

             SECTION 4.5. Holdback Agreement. If any registration under Article
III shall be in connection with an underwritten public offering, Company and
Parent shall not, and Parent shall cause each other member of the Parent Group
not to, effect any public sale or distribution, including any sale pursuant to
Rule 144 under the Securities Act, of any Equity Securities of the Company
(other than as part of such underwritten public offering), within seven days
before, or 90 days (or such lesser period as the managing underwriters may
permit) after, the effective date of any such registration pursuant to Article
III (except as part of any such registration or sale).

                                   ARTICLE V

                                  MISCELLANEOUS

             SECTION 5.1. Termination. This Agreement shall terminate on
December 31, 2000 unless it shall have become effective prior to that date
pursuant to Section 5.10. Following the Closing (if any), this Agreement shall
terminate at the earlier of (a) eight years from the date of the Closing and (b)
the later of (i) such time as Parent is no longer entitled to a Parent
Representative pursuant to the terms of Section 2.1(a) or (ii) such time as all
of the members of the Parent Group, in the aggregate, hold less than 1.5 million
shares of Retained Stock. No such termination shall relieve either party from
any liability for the breach of any of the agreements set forth in this
Agreement.

             SECTION 5.2. Amendments and Waivers. Except as otherwise provided
herein, no modification, amendment or waiver of any provision of this Agreement
shall be effective against either party hereto unless such modification,
amendment or waiver is approved in writing by such party. The failure of a party
to enforce any of the provisions of this Agreement shall in no way be construed
as a waiver of such provisions and shall not affect the right of such party
thereafter to enforce each and every provision of this Agreement in accordance
with its terms.

             SECTION 5.3. Successors, Assigns and Third Party Beneficiaries; No
Assignment. This Agreement shall bind and inure to the benefit of and be
enforceable by the parties hereto and their respective successors and permitted
assigns. Neither this Agreement nor any right, remedy, obligation or liability
arising hereunder or by reason hereof shall be assignable by either party
without the prior written consent of the other party.

             SECTION 5.4. Notices. All notices required or permitted hereunder
shall be in writing and shall be deemed effectively given (a) upon personal
delivery to the party to be notified, (b) when sent by confirmed telex or
facsimile if sent during normal business hours of the recipient or, if not, then
on the next Business Day, (c) five days after having been sent by registered or
certified mail, return receipt requested, postage prepaid or (d) one Business
Day after deposit with a nationally recognized overnight courier, specifying
next day delivery, with written verification of receipt. All communications
shall be sent as follows:

             (i) to the Company at:
<PAGE>   22
                                                                              19

                           Express Scripts, Inc.
                           13900 Riverport Drive
                           St. Louis, MO 63043
                           Attention: President
                           Fax No.:  314-770-1581

                           With a copy to:

                           Express Scripts, Inc.
                           13900 Riverport Drive
                           St. Louis, MO 63043
                           Attention: General Counsel
                           Fax No.:  314-702-7120;

              (ii)         to Parent at:

                           New York Life Insurance Company
                           51 Madison Avenue
                           New York, NY 10010
                           Attention:  President
                           Fax No:  212-576-4545

                           With a copy to:

                           New York Life Insurance Company
                           51 Madison Avenue
                           New York, NY 10010
                           Attention:  General Counsel
                           Fax No:  212-576-6886; or

             (iii)         to such other address for either party as it may
                           specify by like notice.

             SECTION 5.5. Further Assurances. At any time or from time to time
after the date hereof, the parties agree to cooperate with each other, and at
the request of any other party, to execute and deliver any further instruments
or documents and to take all such further action as the other party may
reasonably request in order to evidence or effectuate the consummation of the
transactions contemplated hereby and to otherwise carry out the intent of the
parties hereunder.

             SECTION 5.6. Entire Agreement. This document embodies the complete
agreement and understanding among the parties hereto with respect to the subject
matter hereof and supersedes any prior understandings, agreements or
representations by or between the parties, written or oral, that may have
related to the subject matter hereof in any way.

             SECTION 5.7. Delays or Omissions. It is agreed that no delay or
omission to exercise any right, power or remedy accruing to a party, upon any
breach, default or
<PAGE>   23
                                                                              20

noncompliance by the other party under this Agreement, shall impair any such
right, power or remedy, nor shall it be construed to be a waiver of any such
breach, default or noncompliance, or any acquiescence therein, or of or in any
similar breach, default or noncompliance thereafter occurring. It is further
agreed that any waiver, permit, consent or approval of any kind or character on
the part of a party hereto of any breach, default or noncompliance under this
Agreement or any waiver on such party's part of any provisions or conditions of
this Agreement, must be in writing and shall be effective only to the extent
specifically set forth in such writing. All remedies, either under this
Agreement, by Law, or otherwise afforded to a party, shall be cumulative and not
alternative.

             SECTION 5.8. Governing Law; Jurisdiction; Waiver of Jury Trial.
This Agreement shall be governed in all respects by the Laws of the State of New
York. Any suit, action or proceeding with respect to this Agreement may be
brought in any court or before any similar authority in a court of competent
jurisdiction in the State of New York, and the parties hereto hereby submit to
the non-exclusive jurisdiction of such courts for the purpose of such suit,
proceeding or judgment. Each of the parties hereto hereby irrevocably and
unconditionally waives trial by jury in any legal action or proceeding in
relation to this Agreement and for any counterclaim therein.

             SECTION 5.9. Severability. In case any provision of this Agreement
shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

             SECTION 5.10. Effective Date. This Agreement shall automatically
become effective as of the Closing without any further action by either party
hereto.

             SECTION 5.11. Enforcement. Each party hereto acknowledges that
money damages would not be an adequate remedy in the event that any of the
covenants or agreements in this Agreement are not performed in accordance with
its terms, and it is therefore agreed that in addition to and without limiting
any other remedy or right it may have, the non-breaching party will have the
right to an injunction, temporary restraining order or other equitable relief in
any court of competent jurisdiction enjoining any such breach and enforcing
specifically the terms and provisions hereof.

             SECTION 5.12. Titles and Subtitles. The titles of the sections and
subsections of this Agreement are for convenience of reference only and are not
to be considered in construing this Agreement.

             SECTION 5.13. Counterparts; Facsimile Signatures. This Agreement
may be executed in any number of counterparts, each of which shall be an
original, but all of which together shall constitute one instrument. This
Agreement may be executed by facsimile signature(s).
<PAGE>   24
                                                                              21

             IN WITNESS WHEREOF, the parties hereto have executed this
STOCKHOLDER AND REGISTRATION RIGHTS AGREEMENT as of the date set forth in the
first paragraph hereof.

                                      EXPRESS SCRIPTS, INC.

                                      By: /s/ Barrett Toan
                                          -------------------------------
                                          Name:  Barrett Toan
                                          Title: President

                                      NEW YORK LIFE INSURANCE COMPANY

                                      By: /s/ Howard Atkins
                                          ------------------------------
                                          Name:  Howard Atkins
                                          Title: Executive Vice President and
                                                   Chief Financial Officer<PAGE>   1
                                                                     EXHIBIT 4.3

                           ASSET ACQUISITION AGREEMENT

                          DATED AS OF OCTOBER 17, 2000

                                     BETWEEN

                       NYLIFE HEALTHCARE MANAGEMENT, INC.,

                             EXPRESS SCRIPTS, INC.,

                                   NYLIFE LLC,

                                       AND

                         NEW YORK LIFE INSURANCE COMPANY
<PAGE>   2
                           ASSET ACQUISITION AGREEMENT

         ASSET ACQUISITION AGREEMENT (this "AGREEMENT"), dated as of October 17,
2000, by and among NYLIFE HEALTHCARE MANAGEMENT, INC., a Delaware corporation
("NYLIFE"), EXPRESS SCRIPTS, INC., a Delaware corporation ("ESI"), NYLIFE LLC, a
Delaware limited liability company, and NEW YORK LIFE INSURANCE COMPANY, a
mutual insurance company organized under the laws of the State of New York
("NYL") (NYL, NYLIFE and NYLIFE LLC are collectively referred to herein as the
"NYLIFE COMPANIES"). Each of the NYLIFE Companies and ESI may be referred to
herein as a "PARTY" and any of such entities may be referred to herein as the
"PARTIES."

                                    RECITALS

         ESI desires to acquire and accept, and NYLIFE desires to grant and
transfer, the Acquired Assets (as hereinafter defined) in a transaction
qualifying as a "reorganization" under Section 368(a)(1)(C) of the Internal
Revenue Code of 1986, as amended.

         NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Parties, intending to be
legally bound, hereby agree as follows:

                                    ARTICLE I

                          DEFINITIONS AND OTHER MATTERS

1.1      CERTAIN DEFINITIONS

         "ACQUIRED ASSETS" shall mean 15,020,000 shares of Class B common stock,
$.01 par value per share of ESI, which constitutes all or substantially all of
the assets of NYLIFE.

         "ACQUISITION CONSIDERATION" shall have the meaning ascribed to such
term in Section 2.2 to this Agreement.

         "AGREEMENT" shall have the meaning ascribed to such term in the
introductory paragraph of this Agreement.

         "CLASS A COMMON STOCK" shall have the meaning ascribed to such term in
Section 2.2 of this Agreement.

         "CLOSING" shall have the meaning ascribed to such term in Section 3.1
of this Agreement.

         "CLOSING DATE" shall have the meaning ascribed to such term in Section
3.1 of this Agreement.
<PAGE>   3
         "CLOSING NOTICE" shall have the meaning ascribed to such term in
Section 3.1 of this Agreement.

         "CONSENT" shall mean any consent, approval, authorization, waiver,
permit, grant, franchise, concession, agreement, license, exemption or order of,
registration, certificate, declaration or filing with, or report or notice to
any Person or Governmental Authority.

         "CONTRACT" means any agreement, contract, obligation, promise or
undertaking (whether written or oral and whether express or implied) that is
legally binding.

         "ESI" shall have the meaning ascribed to such term in the introductory
paragraph of this Agreement.

         "EXCLUDED LIABILITIES" shall mean (i) any Tax liability relating to,
pertaining to, imposed on or arising out of either NYLIFE or the Acquired Assets
with respect to any period (or portion thereof) ending on or prior to the
Closing Date, (ii) any Taxes of any member of any affiliated, consolidated,
combined or unitary group of which NYLIFE was, at any time, a member incurred by
ESI or any of its affiliates under Treasury Regulation 1.1502-6 (or any similar
provision of state, local or foreign law), or as a transferee or successor, by
contract or otherwise, and (iii) any payments required to be made after the
Closing Date under any Tax sharing, Tax indemnity, Tax allocation or similar
contracts (whether or not written) to which NYLIFE was obligated, or was a
party, on or prior to the Closing Date.

         "GOVERNMENTAL AUTHORITY" shall mean any (a) nation, state, county,
city, town, village, district or other jurisdiction of any nature; (b) federal,
state, local, municipal, foreign or other government; (c) governmental or
quasi-governmental authority of any nature (including any governmental agency,
branch, department, official, or entity and any court or other tribunal); (d)
multi-national organization or body; or (e) body exercising, or entitled to
exercise, any administrative, executive, judicial, legislative, police,
regulatory or taxing authority or power of any nature.

         "LEGAL REQUIREMENT" means any federal, state, local, municipal,
foreign, international, multinational, or other administrative order,
constitution, law, ordinance, principle of common law, regulation, statute or
treaty.

         "LIEN" shall mean any lien, encumbrance, hypothecation, right of
others, proxy, voting trust or similar arrangement, pledge, security interest,
collateral security agreement, limitations on voting rights, limitations on
rights of ownership filed with any Governmental Authority, claim, charge,
equities, mortgage, pledge, objection, title defect, title retention agreement,
option, restrictive covenant, restriction on transfer, right of first refusal,
right of first offer, statutory or contractual preemptive right or any
comparable interest or right created by or arising under any Legal Requirement,
of any nature whatsoever.

         "NYL" shall have the meaning ascribed to such term in the introductory
paragraph of this Agreement.

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<PAGE>   4
         "NYLIFE" shall have the meaning ascribed to such term in the
introductory paragraph of this Agreement.

         "NYLIFE COMPANIES" shall have the meaning ascribed to such term in the
introductory paragraph of this Agreement.

         "PERSON" shall mean any natural person, company, corporation, limited
liability company, association, partnership, organization, business, firm, joint
venture, trust, unincorporated organization or any other entity or organization.

         "RECEIPT" shall mean a Receipt, dated the Closing Date, executed by
each of ESI and NYLIFE, in substantially the form attached as Exhibit A hereto.

         "RELATED AGREEMENTS" shall mean the Receipt and any other agreements,
instruments or certificates delivered hereunder or in connection with the
transactions contemplated hereby.

         "STOCKHOLDER AGREEMENT" shall mean the Stockholder and Registration
Rights Agreement, dated as of October 6, 2000, between ESI and New York Life
Insurance Company, as amended from time to time.

         "TAX" OR "TAXES" shall mean all taxes of any kind, including those on
or measured by or referred to as income, gross receipts, sales, use ad valorem,
franchise, profits, license, withholding, payroll, employment, excise,
severance, stamp, occupation, premium, value added, property or windfall profits
taxes, customs, duties or similar fees, assessments or charges of any kind
whatsoever, together with any interest and any penalties, additional to tax or
additional amounts imposed by any Governmental Authority, domestic or foreign.

         "TAX RETURN" shall mean any return, report, or statement required to be
filed with any Governmental Authority with respect to Taxes.

                                   ARTICLE II

                              ACQUISITION OF ASSETS

2.1      ACQUISITION OF ASSETS

         Upon the terms and subject to the conditions set forth herein, in
exchange for the Acquisition Consideration, NYLIFE agrees to grant, convey,
assign, transfer and deliver to ESI on the Closing Date, and ESI agrees to
acquire and accept from NYLIFE on the Closing Date, all right, title and
interest of NYLIFE in, to and under the Acquired Assets. For the avoidance of
doubt, it is also agreed that NYLIFE LLC will retain, and ESI shall not assume,
the Excluded Liabilities.

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<PAGE>   5
2.2      PAYMENT OF ACQUISITION CONSIDERATION

         The acquisition consideration for the Acquired Assets is 15,020,000
shares of the Class A common stock, $.01 par value per share ("CLASS A COMMON
STOCK"), of ESI (the "ACQUISITION CONSIDERATION"). The Acquisition Consideration
shall be issued to NYLIFE in one or more stock certificates at the Closing.

                                   ARTICLE III

                                     CLOSING

3.1      CLOSING

         Subject to the satisfaction of the conditions set forth in Article V,
the closing of the transactions contemplated hereby (the "CLOSING") shall take
place at the offices of Cahill Gordon & Reindel, 80 Pine Street, New York, New
York 10005 at 9:00 a.m. (New York time) (or such other place and time as may be
specified by NYLIFE) on the date (the "CLOSING DATE") specified in a written
notice (the "CLOSING NOTICE") delivered by NYLIFE to ESI at the facsimile number
specified on the signature page hereto which Closing Date may be the date of the
Closing Notice.

3.2      DELIVERY OBLIGATIONS OF NYLIFE

         At the Closing, NYLIFE shall deliver to ESI: (i) the Acquired Assets,
duly endorsed in blank, in form satisfactory to ESI and with all required stock
transfer tax stamps attached or, if applicable, an affidavit of indemnity and
loss relating to the Acquired Assets; and (ii) the Receipt, executed by a duly
authorized officer on behalf of NYLIFE.

3.3      DELIVERY OBLIGATIONS OF ESI

         At the Closing, ESI shall deliver to NYLIFE: (i) stock certificate(s)
representing the Acquisition Consideration registered in the name of NYLIFE; and
(ii) the Receipt, executed by a duly authorized officer on behalf of ESI.

3.4      AMENDMENT OF STOCKHOLDER AGREEMENT AND RELATED MATTERS

         Automatically, effective at the Closing, New York Life Insurance
Company and the Company hereby amend the Stockholder Agreement as follows: (i)
to delete Section 2.3 thereof in its entirety; (ii) to amend and restate the
third and fourth paragraphs under the caption "RECITALS" of the Stockholders
Agreement to read in their entirety as follows:

                  "The Company, at the request of Parent, intends to prepare and
                  file with the SEC (as defined below) a registration statement
                  relating to the public offering (the "Stock Offering") of up
                  to 6,900,000 shares of Class A Common Stock, to be acquired by
                  the Stockholder in accordance with

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<PAGE>   6
                  the terms of the Asset Acquisition Agreement, dated as of
                  October 17, 2000 (the "Asset Purchase Agreement"), among
                  NYLIFE HealthCare Management, Inc., NYLIFE LLC, the Company
                  and Parent).

                  Parent intends to prepare and file, or cause to be prepared
                  and filed, with the SEC a registration statement relating to
                  the public offering (the "Trust Offering") by the Express
                  Scripts Automatic Exchange Security Trust (the "Trust") of
                  securities which may be exchanged by the Trust for, among
                  other things, cash or shares of Class A Common Stock."

; (iii) to amend the fifth paragraph under the caption "RECITALS" of the
Stockholder Agreement by adding words "the Retained Stock (as defined below)"
immediately following the word "own" and deleting the remainder of such
paragraph; (iv) to amend and restate the definition of "Retained Stock" in
Section 1.1 of the Stockholder Agreement to read in its entirety as follows:

                  "Retained Stock" means the shares of Class A Common Stock
                  included in the Acquisition Consideration (as defined in the
                  Asset Purchase Agreement) other than the Trust Stock and the
                  shares of Class A Common Stock sold by the Parent Group in the
                  Stock Offering, plus (from and after the date of the
                  termination of the Trust) the shares of Trust Stock in excess
                  of the number of shares of Trust Stock necessary to settle the
                  Parent Group's delivery obligations pursuant to the purchase
                  agreement entered into in connection with the Trust Offering
                  (whether or not the Trust Stock is used to settle such
                  obligations); provided that any such excess shares of Trust
                  Stock are released from the collateral arrangements entered
                  into by Parent or any other member of the Parent Group in
                  connection with the Trust Offering. References herein to
                  numbers of shares of Retained Stock shall be appropriately
                  adjusted to give effect to any stock split, reverse stock
                  split, stock dividend or similar recapitalization event, and
                  any merger, consolidation, exchange or other similar
                  reorganization or business combination involving the Company
                  occurring after the Closing."

; (v) to amend and restate the definition of "Trust Stock" in Section 1.1 of the
Stockholder Agreement to read in its entirety as follows:

                  "Trust Stock" means the maximum number of shares of Class A
                  Common Stock deliverable by the Parent Group pursuant to the
                  securities sold by the Trust in the Trust Offering."

; and (vi) to amend clause (iii) of Section 2.2(a) of the Stockholder Agreement
to delete the reference to "clause (ii)" and replace it with "clauses (ii) and
(iii)."

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<PAGE>   7
                                   ARTICLE IV

                    REPRESENTATIONS, WARRANTIES AND COVENANTS

4.1      REPRESENTATIONS AND WARRANTIES OF NYLIFE

         The NYLIFE Companies hereby, jointly and severally, represent, warrant
and covenant to ESI, with respect to the transactions contemplated herein that:

         (a)      Organization and Authority of the NYLIFE Companies.

                  (i)      NYLIFE is a corporation duly organized, validly
                           existing and in good standing under the laws of the
                           State of Delaware and has the requisite corporate
                           power and authority to enter into and perform this
                           Agreement and the Related Agreements to which it is a
                           party and the transactions herein and therein
                           contemplated.

                  (ii)     NYLIFE LLC is a limited liability company duly
                           organized, validly existing and in good standing
                           under the laws of the State of Delaware and has the
                           requisite limited liability company power and
                           authority to enter into and perform its obligations
                           under this Agreement and the Related Agreements to
                           which it is a party and the transactions herein and
                           therein contemplated.

                  (iii)    NYL is a mutual insurance company duly organized,
                           validly existing and in good standing under the laws
                           of the State of New York and has the requisite
                           [mutual insurance company] power and authority to
                           enter into and perform its obligations under this
                           Agreement and the Related Agreements to which it is a
                           party and the transactions herein and therein
                           contemplated.

         (b) Authorization of Agreement. The execution, delivery and performance
by each of the NYLIFE Companies of this Agreement and the Related Agreements to
which it is a party have been duly authorized by all requisite corporate,
limited liability company or mutual insurance company action, as the case may
be. This Agreement and the Related Agreements to which it is a party have been
duly executed and delivered by each of the NYLIFE Companies and constitute
legal, valid and binding obligations of each of the NYLIFE Companies enforceable
against each of the NYLIFE Companies in accordance with their respective terms,
except as may be limited by bankruptcy or similar laws affecting creditors'
rights generally and general principles of equity.

         (c) No Conflicts. The execution, delivery and performance of this
Agreement and the Related Agreements to which it is a party by each of the
NYLIFE Companies do not violate, breach, conflict with, contravene or cause a
default under: (i) the respective organization document of the NYLIFE Companies;
(ii) any Contract to which any of the NYLIFE Companies is a party or by which it
or its property or any of the Acquired Assets is bound; or (iii) any judicial,
administrative or regulatory order, judgment or decree or arbitration award to
which any of the NYLIFE Companies is a party or by which it or its property or

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<PAGE>   8
any of the Acquired Assets is bound. No Consent from any Governmental Authority
or any other Person is required in connection with the execution, delivery or
performance by any of the NYLIFE Companies of this Agreement or the Related
Agreements to which it is a party.

         (d) No Liens. Upon the consummation of the transactions contemplated by
this Agreement and the Related Agreements, ESI shall acquire good and valid
title to all of the Acquired Assets, free and clear of all Liens.

         (e) No Brokers. Neither of the NYLIFE Companies has incurred any
obligation or liability, contingent or otherwise, for brokers' or finders' fees
or commissions in connection with the transactions contemplated by this
Agreement.

         (f) Acquired Assets. The Acquired Assets are the only shares of Class B
common stock, $.01 par value per share, of ESI held by the NYLIFE Companies and
any other direct or indirect subsidiary of NYL.

         (g) No Other Representations and Warranties. Except as set forth in
this Article III, neither of the NYLIFE Companies makes representations or
warranties whether express or implied.

4.2      REPRESENTATIONS AND WARRANTIES OF ESI

         ESI hereby represents, warrants and covenants to the NYLIFE Companies,
with respect to the transactions contemplated herein that:

         (a) Organization and Authority of ESI. ESI is a corporation duly
organized, validly existing and in good standing under the laws of the State of
Delaware and has the corporate power and authority to enter into and perform
this Agreement and the Related Agreements to which it is a party and the
transactions herein and therein contemplated.

         (b) Authorization of Agreement. The execution, delivery and performance
by ESI of this Agreement and the Related Agreements to which it is a party have
been duly authorized by all requisite corporate action. This Agreement and the
Related Agreements to which it is a party have been duly executed and delivered
by ESI and constitute legal, valid and binding obligations of ESI enforceable
against ESI in accordance with their respective terms, except as may be limited
by bankruptcy or similar laws affecting creditors' rights generally and general
principles of equity.

         (c) No Conflicts. The execution, delivery and performance of this
Agreement and the Related Agreements to which it is a party by ESI do not
violate, breach, conflict with, contravene or cause a default under: (i) the
certificate of incorporation or bylaws of ESI; (ii) any Contract to which ESI is
a party or by which it or its property is bound; or (iii) any judicial,
administrative or regulatory order, judgment or decree or arbitration award to
which ESI is a party or by which it or its property is bound. No Consent of any
Governmental Authority or any other Person is required in connection with the
execution, delivery or performance by ESI of this Agreement or the Related
Agreements.

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<PAGE>   9
         (d) Acquisition Consideration. When issued at the Closing, the shares
of Class A Common Stock comprising the Acquisition Consideration will be duly
authorized, validly issued, fully paid and nonassessable shares of Class A
Common Stock, and the issuance of such shares will not be subject to any
preemptive or similar rights. At the Closing, the Acquisition Consideration will
be acquired by NYLIFE free and clear of any Liens.

         (e) No Brokers. ESI has not incurred any obligation or liability,
contingent or otherwise, for brokers' or finders' fees or commissions in
connection with the transactions contemplated by this Agreement.

         (f) No Other Representations and Warranties. Except as set forth in
this Article IV, ESI makes no representations or warranties whether express or
implied.

4.3      TAX COVENANT

         NYLIFE and ESI agree that this transaction, coupled with a subsequent
liquidation of NYLIFE, is intended to qualify as a "reorganization" under
Section 368(a)(1)(C) of the Internal Revenue Code of 1986, as amended, and that
neither of them will take any action that would prevent the transaction from so
qualifying or file any Tax Return that reports this transaction as other than
such a "reorganization", unless otherwise required by applicable law. None of
ESI (or any related party to ESI) have any plan or arrangement to acquire all or
any part of the Acquisition Consideration, other than purchases in the open
market pursuant to a stock repurchase plan of ESI which was announced before the
date of this Agreement.

4.4      NASDAQ LISTING

         ESI agrees to take all actions required to cause the shares included in
the Acquisition Consideration to have been approved for inclusion in the Nasdaq
National Market on the Closing Date; provided that any such actions shall be at
the sole cost and expense of NYL (other than as contemplated by the Stockholder
Agreement).

                                    ARTICLE V

                               CLOSING CONDITIONS

5.1      CONDITION TO THE OBLIGATIONS OF NYLIFE

         The obligations of NYLIFE to consummate the transactions contemplated
by this Agreement are subject to the receipt of a certificate duly executed by
an authorized officer of ESI certifying that the representations and warranties
of ESI under this Agreement are true and correct in all material respects as of
the Closing Date or waiver of this condition by NYLIFE.

                                       8
<PAGE>   10
5.2      CONDITION TO THE OBLIGATIONS OF ESI

         The obligations of ESI to consummate the transactions contemplated by
this Agreement are subject to the receipt of a certificate duly executed by an
authorized officer of NYLIFE certifying that the representations and warranties
of NYLIFE under this Agreement are true and correct in all material respects as
of the Closing Date or waiver of this condition by ESI.

5.3      GENERAL

         NYLIFE and ESI agree to deliver the certificates referred to in
Sections 5.1 and 5.2 at the Closing.

                                   ARTICLE VI

                                 INDEMNIFICATION

6.1      TAX INDEMNIFICATION OF ESI

         (a) NYL and NYLIFE LLC jointly and severally covenant and agree to be
responsible for, defend, indemnify and hold harmless ESI from and against, and
to pay, (i) any Tax imposed on or with respect to ESI attributable to, arising
from or relating to the transactions contemplated by Article II of this
Agreement and (ii) attributable to, arising from or relating to the Excluded
Liabilities. If the payment of indemnification under this Section 6.1
("INDEMNITY CLAIM") gives rise to a currently realizable Tax Benefit (as defined
below) to ESI, the indemnity payment shall be reduced by the amount of the Tax
Benefit available to ESI. The net amount of any loss, liability, claim, damage,
expense or Tax for which indemnification is provided under this Section 6.1
shall be increased to take account of any net Tax cost incurred by ESI arising
from the receipt of indemnity payments hereunder. To the extent such Indemnity
Claim does not give rise to a currently realizable Tax Benefit, if the amount
with respect to which any Indemnity Claim is made gives rise to a subsequently
realized Tax Benefit to ESI, ESI shall refund to NYL or NYLIFE LLC, as
appropriate, the amount of such Tax Benefit when, as and if actually realized.
For the purposes of this Agreement, any subsequently realized Tax Benefit shall
be treated as though it were a reduction in the amount of the initial Indemnity
Claim, and the liabilities of the parties shall be redetermined as though both
occurred at or prior to the time of the indemnity payment. For purposes of this
Section 6.1, a "TAX BENEFIT" means an amount by which the Tax liability of ESI
is actually reduced plus any related interest received from the relevant
Governmental Authority. Where ESI has other losses, deductions, credits or items
available to it, the Tax Benefit from any losses, deductions, credits or items
relating to the Indemnity Claim shall be deemed to be realized last after any
other losses, deductions, credits or items are realized. For the purposes of
this Section 6.1, a Tax Benefit is "currently realizable" to the extent that
such Tax Benefit will be actually realized in the current taxable period or year
or in any Tax return with respect thereto (including through a carryback to a
prior taxable period) or in any taxable period or year prior to the date of the
Indemnity Claim. In the event that there should be a determination disallowing
the Tax

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Benefit, the indemnifying party shall be liable to refund to ESI the amount of
any related reduction previously allowed or payments previously made to the
indemnifying party pursuant to this Section 6.1. The amount of the refunded
reduction or payment shall be deemed a payment under this Section 6.1 of this
Agreement and thus shall be paid subject to any applicable reductions under this
Section 6.1.

         (b) In the event that ESI receives a refund or credit of any Tax for
which NYLIFE LLC or NYL has made a payment pursuant to Section 6.1(a), then ESI
(i) shall promptly pay to NYLIFE LLC or NYL the amount of such refund (including
any interest received by ESI in respect of such refunded Tax), or (ii) shall pay
to NYLIFE LLC or NYL the amount of such credit at such time as such credit
actually reduces the Tax liability of ESI; provided, however, that ESI shall not
be required to pay to NYLIFE LLC or NYL any refund or credit of Taxes that
results from the carryback to any pre-Closing Date Tax period of any net
operating loss, capital loss or tax credit attributable to ESI. In the event
that any refund or credit of Taxes for which a payment has been made pursuant to
this Section 6.1(b) is subsequently reduced or disallowed, NYLIFE LLC or NYL
shall indemnify and hold harmless ESI for any Tax liability, including interest
and penalties, assessed against ESI by reason of such reduction or disallowance.

6.2  TAX CONTESTS

         (a) If any claim for Tax is asserted by any Governmental Authority
against ESI that, if successful, would result in an Indemnity Claim the parties
hereto agree to abide by the following procedures in handling any such claim:

                  (i)      Each party shall, upon receiving any notice of an
                           assertion of a claim for Taxes that would result in
                           an Indemnity Claim, notify the other party in writing
                           of such assertion of a claim for Taxes within a
                           reasonable period of time. In the event that notice
                           of such claim is not given to NYLIFE LLC or NYL
                           within a sufficient period of time or in reasonable
                           detail to apprise NYLIFE LLC or NYL of the nature of
                           the claim (in each instance taking into account the
                           facts and circumstances with respect to such claim),
                           NYLIFE LLC or NYL shall not be liable to ESI under
                           Section 6.1(a) for such claim to the extent, if any,
                           that the rights of NYLIFE LLC or NYL with respect to
                           such claim are actually materially prejudiced.

                  (ii)     NYLIFE LLC or NYL shall control all proceedings taken
                           in connection with contesting any such claim. ESI
                           shall take such action in connection with contesting
                           such claim as NYLIFE LLC or NYL shall reasonably
                           request in writing from time to time; provided that
                           (A) within a reasonable period (or such earlier date
                           that any payment of Taxes is due by ESI) after the
                           notice described in Section 6.2(a)(i) has been
                           delivered to NYLIFE LLC or NYL, NYLIFE LLC or NYL
                           requests that such claim be contested; (B) NYLIFE LLC
                           and/or NYL shall have agreed to pay on an after-Tax
                           basis to ESI on demand all costs and expenses in
                           connection with

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<PAGE>   12
                           contesting such claim (or appeal), including, without
                           limitation, reasonable attorneys' and accountants'
                           fees and disbursements; (C) if ESI is requested or
                           shall determine to pay the Tax claimed and sue for a
                           refund, NYLIFE LLC or NYL shall have advanced to ESI,
                           on an interest-free basis (and at no additional tax
                           cost to ESI), the amount of such claim; (D) ESI is
                           allowed to participate in the contest of such claim
                           to the extent that the resolution could have a
                           material adverse effect on ESI, and (E) NYLIFE LLC or
                           NYL shall not settle or compromise such Indemnity
                           Claim without the prior written consent of ESI if the
                           settlement or compromise would have a material
                           adverse effect on ESI for a post-Closing period. In
                           the case of any such claim referred to above, ESI
                           shall give to NYLIFE LLC or NYL any information
                           reasonably requested by NYLIFE LLC or NYL relating to
                           such claim and otherwise shall cooperate with NYLIFE
                           LLC or NYL in good faith in order to contest
                           effectively any such claim.

         (b) If, after actual receipt by ESI of an amount advanced by NYLIFE LLC
or NYL pursuant to clause C of Section 6.2(a)(ii), the extent of the liability
of ESI with respect to the indemnified matter shall be established, ESI shall
promptly pay to NYLIFE LLC or NYL all or the portion of any refund received by
or credited to ESI with respect to the indemnified matter (together with any
interest paid or credit thereon by the relevant Governmental Authority) reduced
by any liability for Taxes incurred by ESI in respect of such payment.

                                   ARTICLE VII

                                   TERMINATION

7.1      TERMINATION OF AGREEMENT

         If the Closing shall not have occurred, this Agreement shall terminate
either on (x) at 11:59 p.m. (New York Time) on December 31, 2000, or (y) such
earlier date and time as NYLIFE may specify in a written notice delivered to
ESI.

                                  ARTICLE VIII

                                  MISCELLANEOUS

8.1      ENTIRE AGREEMENT; AMENDMENT

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         This Agreement (together with the Exhibits hereto and Related
Agreements) constitutes the entire agreement between the Parties with respect to
the subject matter contained herein, supersedes all prior oral or written
agreements, commitments or understandings between the Parties with respect
thereto, and cannot be amended, supplemented or otherwise modified except in a
writing executed by each of the Parties.

8.2      GOVERNING LAW

         This Agreement shall be governed by and construed in accordance with
the laws of the State of New York.

8.3      COUNTERPARTS

         This Agreement may be executed in any number of counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

8.4      SUCCESSORS AND ASSIGNS

         This Agreement is intended for the exclusive benefit of the parties
hereto and their respective successors and assigns. Nothing contained in this
Agreement shall be construed as granting any rights or benefits in or to any
third party, and no person shall assert any rights as third-party beneficiary
hereunder.

8.5      CAPTIONS

         The captions in this Agreement are for convenience of reference only
and shall not be given any effect in the interpretation of this Agreement.

8.6      FURTHER ASSURANCES

         On or after the date hereof, NYLIFE and ESI hereby agree to promptly
execute, acknowledge and deliver any other assurances, instruments, agreements,
certificates or other documents and take any other action reasonably requested
by the other party hereto to effect the transactions contemplated hereby.

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<PAGE>   14
         IN WITNESS WHEREOF, the Parties have caused this Agreement to be
executed by their officers or other duly authorized representatives as of the
date first above written.

                              EXPRESS SCRIPTS, INC.

                              By:      /s/ George Paz
                                       -----------------------------------------
                                       Name:  George Paz
                                       Title: Senior Vice President and Chief
                                              Financial Officer

                                       Facsimile No.:  314-702-7037
                                                       -------------------------

                              NYLIFE HEALTHCARE
                              MANAGEMENT, INC.

                              By:      /s/ Richard M. Kernan, Jr.
                                       -----------------------------------------
                                       Name:  Richard M. Kernan, Jr.
                                       Title: Senior Vice President

                              NYLIFE LLC

                              By:      /s/ Richard M. Kernan, Jr.
                                       -----------------------------------------
                                       Name:  Richard M. Kernan, Jr.
                                       Title: Chairman

                              NEW YORK LIFE INSURANCE COMPANY

                              By:      /s/ Richard M. Kernan, Jr.
                                       -----------------------------------------
                                       Name:  Richard M. Kernan, Jr.
                                       Title: Executive Vice President and
                                              Chief Investment Officer

                                       13
<PAGE>   15
                                                                       EXHIBIT A

                                 FORM OF RECEIPT

         Reference is hereby made to that certain Asset Acquisition Agreement
(the "AGREEMENT"), dated as of the date hereof, between Express Scripts, Inc.
("ESI") NYLIFE HealthCare Management, Inc. ("NYLIFE"), NYLIFE LLC and New York
Life Insurance Company. Capitalized terms used but not defined herein shall have
the respective meanings ascribed to them in the Agreement.

         ESI hereby acknowledges receipt, on the date hereof, of the Acquired
Assets referenced in Section 2.1 of the Agreement.

         NYLIFE hereby acknowledges receipt from ESI of the Acquisition
Consideration.

Date:    __________ __, 2000

                                 EXPRESS SCRIPTS, INC.

                                 By:      /s/ George Paz
                                          ------------------------------------
                                          Name:  George Paz
                                          Title: Senior vice President and
                                                 Chief Financial Officer

                                 NYLIFE HEALTHCARE
                                 MANAGEMENT, INC.

                                 By:      /s/ Richard M. Kernan, Jr.
                                          ------------------------------------
                                          Name:  Richard M. Kernan, Jr.
                                          Title: Senior Vice President

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