Filed by Express Scripts, Inc.
Pursuant to Rule 425 under the Securities Act of 1933

Subject Company: Caremark Rx, Inc.
Commission File No.: 001-14200

Date

Address

Dear :                     :

With only a few days remaining before Caremark stockholders vote on the proposed CVS acquisition of Caremark, I will be unable to meet with you personally. Nevertheless, I wanted to get our message and commitment to this deal front and center with your team. We remain resolute that an Express Scripts and Caremark combination has great potential and is clearly be the best value proposition for Caremark shareholders.

With that being said, our first responsibility is to our stockholders. It is for that reason that I cannot with good conscience offer more consideration for the deal without an opportunity to conduct due diligence. There is no way around it, the best case scenario for Express Scripts and Caremark stockholders is for bidders to have equal information and then engage in a competitive bid process.

The enclosed deck we are sharing with investors once again provides the compelling proof points for an Express Scripts/Caremark combination.

	•		ESRX offers more certainty of value and better currency.
	•		ESRX has a strong record of innovation and execution.
	•		ESRX profit generators are powerful with room to run.
	•		ESRX confirms bullish outlook by increasing 2007 EPS guidance.

Our proposal is based on the undeniable strategic rationale of independence and proven value generation. Synergies are identifiable and achievable, while strong free cash flow would allow for rapid debt reduction and share repurchase. We offer a superior currency, greater certainty of value and a management team with a history of earnings growth, superior stockholder returns and successful acquisitions and integrations.

Vote the GOLD proxy card AGAINST the flawed process.

Caremark stockholders deserve better. The potential of an Express Scripts/Caremark combination offers Caremark stockholders greater value today and in the future.

If you have any questions, please feel free to call me directly at 314.702.7548.

Sincerely,

Safe Harbor Statement

This press release contains forward-looking statements, including, but not limited to, statements related to the Company’s plans, objectives, expectations (financial and otherwise) or intentions. Actual results may differ significantly from those projected or suggested in any forward-looking statements. Factors that may impact these forward-looking statements include but are not limited to:

	•		uncertainties associated with our acquisitions, which include integration risks and costs, uncertainties associated with client retention and repricing of client contracts, and uncertainties associated with the operations of acquired businesses
	•		costs and uncertainties of adverse results in litigation, including a number of pending class action cases that challenge certain of our business practices
	•		investigations of certain PBM practices and pharmaceutical pricing, marketing and distribution practices currently being conducted by the U.S. Attorney offices in Philadelphia and Boston, and by other regulatory agencies including the Department of Labor, and various state attorneys general
	•		changes in average wholesale prices (“AWP”), which could reduce prices and margins, including the impact of a proposed settlement in a class action case involving First DataBank, an AWP reporting service
	•		uncertainties regarding the implementation of the Medicare Part D prescription drug benefit, including the financial impact to us to the extent that we participate in the program on a risk-bearing basis, uncertainties of client or member losses to other providers under Medicare Part D, and increased regulatory risk
	•		uncertainties associated with U.S. Centers for Medicare & Medicaid’s (“CMS”) implementation of the Medicare Part B Competitive Acquisition Program (“CAP”), including the potential loss of clients/revenues to providers choosing to participate in the CAP
	•		our ability to maintain growth rates, or to control operating or capital costs
	•		continued pressure on margins resulting from client demands for lower prices, enhanced service offerings and/or higher service levels, and the possible termination of, or unfavorable modification to, contracts with key clients or providers
	•		competition in the PBM and specialty pharmacy industries, and our ability to consummate contract negotiations with prospective clients, as well as competition from new competitors offering services that may in whole or in part replace services that we now provide to our customers
	•		results in regulatory matters, the adoption of new legislation or regulations (including increased costs associated with compliance with new laws and regulations), more aggressive enforcement of existing legislation or regulations, or a change in the interpretation of existing legislation or regulations
	•		increased compliance relating to our contracts with the DoD TRICARE Management Activity and various state governments and agencies
	•		the possible loss, or adverse modification of the terms, of relationships with pharmaceutical manufacturers, or changes in pricing, discount or other practices of pharmaceutical manufacturers or interruption of the supply of any pharmaceutical products

	•		the possible loss, or adverse modification of the terms, of contracts with pharmacies in our retail pharmacy network
	•		the use and protection of the intellectual property we use in our business
	•		our leverage and debt service obligations, including the effect of certain covenants in our borrowing agreements
	•		our ability to continue to develop new products, services and delivery channels
	•		general developments in the health care industry, including the impact of increases in health care costs, changes in drug utilization and cost patterns and introductions of new drugs
	•		increase in credit risk relative to our clients due to adverse economic trends
	•		our ability to attract and retain qualified personnel
	•		other risks described from time to time in our filings with the SEC

Risks and uncertainties relating to the proposed transaction that may impact forward-looking statements include but are not limited to:

	•		Express Scripts and Caremark may not enter into any definitive agreement with respect to the proposed transaction
	•		required regulatory approvals may not be obtained in a timely manner, if at all
	•		the proposed transaction may not be consummated
	•		the anticipated benefits of the proposed transaction may not be realized
	•		the integration of Caremark’s operations with Express Scripts may be materially delayed or may be more costly or difficult than expected
	•		the proposed transaction would materially increase leverage and debt service obligations, including the effect of certain covenants in any new borrowing agreements.

We do not undertake any obligation to release publicly any revisions to such forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

Important Information

Express Scripts has filed a proxy statement and proxy supplement in connection with Caremark’s special meeting of stockholders at which the Caremark stockholders will consider the CVS Merger Agreement and matters in connection therewith. Express Scripts stockholders are strongly advised to read that proxy statement and proxy supplement and the accompanying form of GOLD proxy card, as they contain important information. Express Scripts also intends to file a proxy statement in connection with Caremark’s annual meeting of stockholders at which the Caremark stockholders will vote on the election of directors to the board of directors of Caremark. Express Scripts stockholders are strongly advised to read this proxy statement and the accompanying proxy card when they become available, as each will contain important information. Stockholders may obtain each proxy statement, proxy card and any amendments or supplements thereto which are or will be filed with the Securities and Exchange Commission (“SEC”) free of charge at the SEC’s website (www.sec.gov) or by directing a request to MacKenzie Partners, Inc., at 800-322-2885 or by email at expressscripts@mackenziepartners.com.

In addition, this material is not a substitute for the prospectus/offer to exchange and registration statement that Express Scripts has filed with the SEC regarding its exchange

offer for all of the outstanding shares of common stock of Caremark. Investors and security holders are urged to read these documents, all other applicable documents, and any amendments or supplements thereto when they become available, because each contains or will contain important information. Such documents are or will be available free of charge at the SEC’s website (www.sec.gov) or by directing a request to MacKenzie Partners, Inc., at 800-322-2885 or by email at expressscripts@mackenziepartners.com.

Express Scripts and its directors, executive officers and other employees may be deemed to be participants in any solicitation of Express Scripts or Caremark shareholders in connection with the proposed transaction. Information about Express Scripts’ directors and executive officers is available in Express Scripts’ proxy statement, dated April 18, 2006, filed in connection with its 2006 annual meeting of stockholders. Additional information about the interests of potential participants is included in the proxy statement filed in connection with Caremark’s special meeting to approve the proposed merger with CVS and will be included in any proxy statement regarding the proposed transaction. We have also filed additional information regarding our solicitation of stockholders with respect to Caremark’s annual meeting on a Schedule 14A pursuant to Rule 14a-12 on January 9, 2007.