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TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

1.

Description of Plan

The following description of The Schering-Plough Puerto Rico Employees’ Retirement Savings Plan (the “Plan”) is provided for general information purposes only. Participants should refer to the Plan document for more complete information.

General

The Plan is a defined contribution plan established effective April 1, 1990. Schering-Plough Products, L.L.C., a subsidiary of Merck & Co., Inc. (“Merck” or the “Company”), is the Plan Sponsor (the “Sponsor”). The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 ("ERISA").

The Plan is intended to encourage retirement savings by eligible employees of Schering-Plough Products, L.L.C. and any of its affiliated companies that adopt the Plan. Vanguard Fiduciary Trust Company ("Vanguard"), the recordkeeper, is a trust company incorporated under Chapter 10 of the Pennsylvania Banking Code, and a wholly-owned subsidiary of The Vanguard Group, Inc. Banco Popular serves as the Plan’s trustee (the “Trustee").

Participants direct the investment of their contributions into any fund investment option available under the Plan, including Merck common stock. During 2010, the Plan offered 14 registered investment companies (mutual funds) and one separately managed account.

Generally, all Puerto Rico employees of Schering-Plough Products, L.L.C. and Schering-Plough del Caribe, Inc. are eligible to participate in the Plan on the date of employment. Participants may elect to have contributions allocated to any of the investment funds available under the Plan.

The Plan is administered by management committees appointed by the Company’s Chief Executive Officer, the Compensation and Benefits Committee of the Board of Directors of Merck, or their delegates.

Contributions by Participants

The Plan is designed to permit eligible employees to elect to have a portion of their salary contributed to the Plan on their behalf (“Salary Deferral Contributions”). Under the provisions of the Plan, Salary Deferral Contributions can range from 1 percent to 10 percent of the employee’s annual eligible compensation, in increments of 1 percent, subject to certain regulated limits. Any excess participant contributions are returned to the participant.

Contributions by Employer

The Company makes matching contributions (dollar-for-dollar) up to 5 percent of annual eligible compensation for employees who elect to make Salary Deferral Contributions to the Plan.

Participant Accounts

Individual accounts are maintained for each Plan participant. Each participant’s account is credited with contributions and allocations of Plan earnings and charged with withdrawals and losses. Allocations are based on participant earnings or account balances, as defined.

Vesting

Participants have a non-forfeitable right to their contributions and employer matching contributions plus (minus) actual earnings (losses) thereon, all of which vest fully and immediately. Participant contributions and employer matching contributions are participant-directed.

Notes Receivable from Participants

Participants may borrow against their account balances at fixed interest rates determined to be reasonable by the Merck & Co., Inc. Oversight Committee (the "Committee"). Loan terms range from one to five years for a short term loan or up to twenty years for the purchase of a primary residence. The minimum loan is $1,000. Participants may borrow against their account balance up to the lesser of one-half of the account balance or $50,000 (reduced by certain amounts attributable to outstanding loans).

Payment of Benefits

Upon termination of service or in the event of death or total disability, a participant (or the participant’s beneficiary in the event of death) may elect to receive either: (1) a cash lump-sum amount; (2) fixed or variable installments not to exceed the life expectancy of the participant and the participant’s beneficiary; (3) shares of Merck common stock (with respect to amounts invested in Merck Common Stock); or (4) certain combinations of the foregoing.

Participants whose account balances exceed $5,000 can elect to defer the receipt of their account up to age 70 ½.

Small Benefits Payments - Notwithstanding the foregoing, if a participant’s account equals $5,000 or less as of the date of distribution, the account will be paid in a lump-sum.

2.

Summary of Accounting Policies

Basis of Accounting

The accompanying financial statements are prepared on the accrual basis of accounting.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and changes therein, and disclosure of contingent assets and liabilities at the date of the financial statements. Management believes that these estimates are adequate. Actual results could differ from those estimates.

Investment Valuation and Income Recognition

The Plan’s investments are stated at fair value. Purchases and sales of securities are recorded on a trade-date basis. Interest income is recorded as earned. Dividend income is recorded on the ex-dividend date. Dividends recorded in stock are reinvested in common stock units unless an election is made by the participant to receive these dividends in cash.

Notes Receivable from Participants

Notes receivable from participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Delinquent participant loans are reclassified as distributions based upon the terms of the plan document.

Withdrawals and Benefit Payments

Withdrawals and benefit payments are recorded when paid.

Expenses

All plan administration expenses are paid by the Company.

Recently Issued Accounting Standards

Accounting Standards Update 2010-25 (“Update”), issued in September 2010, requires participant loans be classified as notes receivable from participants, segregated from plan investments and measured at their unpaid principal balance plus any accrued but unpaid interest. The amendments in this Update should be applied retrospectively to all prior periods presented, effective for fiscal years ending after December 15, 2010, with early adoption permitted. The Plan adopted this guidance as of December 31, 2010 and reclassified participant loans from plan investments to a component of receivables for both periods presented in the Statements of Net Assets Available for Benefits. Other than the reclassification requirements, the adoption of this standard did not have a material impact on the Plan's financial statements.

In January 2010, the Financial Accounting Standards Board (“FASB”) amended the existing disclosure guidance on fair value measurements, which was effective January 1, 2010, except for disclosures about purchases, sales, issuances, and settlements in the roll forward of activity in Level 3 fair value measurements, which was effective January 1, 2011. Among other things, the updated guidance requires additional disclosure for the amounts of significant transfers in and out of Level 1 and Level 2 measurements and requires certain Level 3 disclosures on a gross basis. Additionally, the updates amend existing guidance to require a greater level of disaggregated information and more robust disclosures about valuation techniques and inputs to fair value measurements. Since the amended guidance requires only additional disclosures, the adoption of the provisions effective January 1, 2010 did not, and for the provisions effective in 2011 will not, impact the Plan’s net assets available for benefits or changes in net assets available for benefits.

In May 2011, the FASB issued ASU 2011-04 Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS (“ASU 2011-04”). ASU 2011-04 is intended to improve the comparability of fair value measurements presented and disclosed in financial statements prepared in accordance with U.S. GAAP and IFRS. The amendments are of two types: (i) those that clarify the Board's intent about the application of existing fair value measurement and disclosure requirements and (ii) those that change a particular principle or requirement for measuring fair value or for disclosing information about fair value measurements. The update is effective for annual periods beginning after December 15, 2011. Plan management is in the process of evaluating the impact of the adoption of this update on the Plan's financial statements.

Risks and Uncertainties

The Plan provides for various investment options in investment securities. Investment securities, in general, are exposed to various risks and may decline in value for a number of reasons, including changes in prevailing interest rates and credit availability, increases in defaults, increases in voluntary prepayments for investments that are subject to prepayment risk under normal market conditions, widening of credit spreads and overall market volatility. Due to the level of risk associated with certain investment securities, it is reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amounts reported in the Statements of Net Assets Available for Benefits.

3.  

Related-Party Transactions

Contributions are transmitted from the Trustee, Banco Popular, to the recordkeeper, Vanguard, which invests cash received, interest and dividend income and makes distributions to the participants. The recordkeeper also administers the collection of interest and principal on notes receivable from participants. These transactions qualify as permitted party-in-interest transactions.

Certain Plan investments are shares of Registered Investment Companies (Mutual Funds) managed by Vanguard. These transactions qualify as permitted party-in-interest transactions. As of December 31, 2010 and 2009, the total market value of investments in the mutual funds managed by Vanguard was $25.9 million and $24.6 million, respectively. During 2010, income from investments managed by Vanguard was $2,255,993.

The Company is also a party-in-interest to the Plan under the definition provided in Section 3(14) of ERISA. Therefore, Plan transactions of Merck common stock qualify as party-in-interest transactions. The market value of investments in Merck’s Common Stock was $5.1 million and $4.8 million at December 31, 2010 and December 31, 2009, respectively. During 2010, income from Merck common stock was $110,195.

Certain administrative functions are performed by officers or employees of the Company or its subsidiaries who may also be participants in the Plan. These actions qualify as permitted party-in-interest activities. No such officer or employee receives compensation from the Plan.

4.

Plan Termination

Although it has not expressed any intent to do so, the Sponsor has the right under the Plan to terminate the Plan subject to the provisions of ERISA. Upon an event of a whole or partial termination of the Plan as defined under the Plan, the Sponsor may direct the Trustee to: (1) distribute the total assets in the affected participants’ accounts to the participants in cash or in-kind as permitted by applicable law; or (2) maintain the assets in The Schering-Plough Puerto Rico Employees’ Retirement Savings Plan Trust (the “Trust”) and make distribution of benefits at such time and manner as though the Plan had not been terminated.

5.

Tax Status

The trust of the Plan is intended to be exempt from taxation under Section 1165(a) of the Puerto Rico Internal Revenue Code of 1995, as amended, (the "PR Code") and pursuant to Section 1022(i)(1) of ERISA under Section 501(a) of the United States Internal Revenue Code of 1986, as amended.

As long as the Plan is qualified under the PR Code and related regulations, participants will generally not be taxed on salary-deferred contributions until the year received. In addition, the earnings attributable to such contributions held by the Trustee are also generally exempt from taxation until the taxable year in which they are withdrawn by or distributed to the participant.

The Plan received a favorable determination letter dated February 18, 1997 issued by the Puerto Rico Department of the Treasury stating that the Plan meets the requirements of Section 1165(a) of the PR Code.

The Plan was amended and restated effective November 4, 2009. However, the Plan’s management, based on advice from the Plan’s tax counsel, believes that the Plan continues to be designed in compliance with the applicable requirements of the PR Code, and the plan administrator believes that the Plan is currently being operated in material compliance with the applicable requirements of the PR Code. Therefore, no provision for income taxes has been included in the Plan’s financial statements.

Accounting principles generally accepted in the United States of America require Plan management to evaluate tax positions taken by the Plan and recognize a tax liability (or asset) if the Plan has taken an uncertain position that more likely than not would not be sustained upon examination by the Internal Revenue Service. The Plan administrator has analyzed the tax positions taken by the Plan, and has concluded that as of December 31, 2010, there are no uncertain positions taken or expected to be taken that would require recognition of a liability (or asset) or disclosure in the financial statements. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The Plan administrator believes it is no longer subject to income tax examinations for years prior to 2008.

6.

Investments

The following investments represented five percent or more of the Plan’s net assets available for benefits at either December 31, 2010, or December 31, 2009:

During 2010, the Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated (depreciated) in value as follows:

7.  

Fair Value Measurements

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Entities are required to use a fair value hierarchy which maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value:

     Level 1 – Quoted prices in active markets for identical assets or liabilities. The Plan’s Level 1 assets primarily include registered investment companies (mutual funds) and common stocks.

     Level 2 – Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

     Level 3 – Unobservable inputs that are supported by little or no market activity and that are financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. The Plan did not hold any Level 3 assets at December 31, 2010 and 2009, respectively.

If the inputs used to measure the financial assets and liabilities fall within more than one level described above, the categorization is based on the lowest level input that is significant to the fair value measurement of the instrument.

Registered Investment Companies (Mutual Funds)

Registered Investment Companies (mutual funds) are valued at their respective net asset values. The net asset values are typically determined by the fund at the close of regular trading on the New York Stock Exchange. Investments in registered investment companies (mutual funds) generally may be redeemed daily.

Common Stocks

Common stocks, for which market quotations are readily available, are generally valued at the last reported sales price on their principal exchange on valuation date, or official close price for certain markets. If no sales are reported for that day, investments are valued at the more recent of (i) the last published sale price or (ii) the mean between the last reported bid and asked prices for long positions, or at fair value as determined in good faith by the Trustee and the Company.