UNITED STATES SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 11-K

ANNUAL REPORT
Pursuant to Section 15(d) of the
Securities Exchange Act of 1934

(Mark One)

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

For the fiscal year ended December 31, 2006

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

For the transition period from                      to                     

MERCK PUERTO RICO EMPLOYEE SAVINGS AND SECURITY PLAN
(Full title of the plan)

MERCK & CO., INC.

(Name of issuer of the securities held pursuant to the plan)

One Merck Drive
P.O. Box 100
Whitehouse Station, New Jersey 08889-0100
(Address of principal executive office)

 

 

Index to Financial Statements and Supplemental Schedule

		Page
Report of Independent Registered Public Accounting Firm			1
Financial Statements:
Statements of Net Assets Available for Benefits as of December 31, 2006 and 2005			2
Statement of Changes in Net Assets Available for Benefits for the year ended December 31, 2006			3
Notes to Financial Statements			4-7
Supplemental Schedule*:
H — Line 4i — Schedule of Assets (Held at End of Year)			8
Signature			9
Exhibit Index			10
Exhibit 23 — Consent of Independent Registered Public Accounting Firm			11

Report of Independent Registered Public Accounting Firm

To the Participants and Administrator of the
Merck Puerto Rico Employee Savings and Security Plan

In our opinion, the accompanying statements of net assets available for benefits and the related statement of changes in net assets available for benefits present fairly, in all material respects, the net assets available for benefits of Merck Puerto Rico Employee Savings and Security Plan (the “Plan”) at December 31, 2006 and 2005, and the changes in net assets available for benefits for the year ended December 31, 2006 in conformity with accounting principles generally accepted in the United States of America. These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits of these statements in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, assessing the accounting principles used and significant estimates made by management and evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

Our audits were conducted for the purpose of forming an opinion on the basic financial statements taken as a whole. The supplemental Schedule of Assets (Held at End of Year) as of December 31, 2006 is presented for the purpose of additional analysis and is not a required part of the basic financial statements but is supplementary information required by the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. This supplemental schedule is the responsibility of the Plan’s management. The supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

/s/ PricewaterhouseCoopers LLP

San Juan, Puerto Rico
June 18, 2007

Merck Puerto Rico Employee Savings and Security Plan

		December 31,
		2006				2005
Assets
Investments
Investments at market value		$	39,265,683			$	31,719,738
Participant loans at cost			1,792,543				1,798,612
Total investments			41,058,226				33,518,350
Receivables
Employer contribution			53,386				27,521
Participant contributions			90,252				90,975
Accrued interest and dividends			178,128				185,805
Total receivables			321,766				304,301
Cash and cash equivalents			29,884				—
Net assets available for benefits		$	41,409,876			$	33,822,651

The accompanying notes are an integral part of these financial statements.

Merck Puerto Rico Employee Savings and Security Plan

		Year Ended
		December 31,
		2006
Additions to net assets attributed to
Investment gain
Net appreciation in market value of investments		$	7,069,156
Dividends and interest			1,738,930
Net investment gain			8,808,086
Contributions to the Plan
By participants			4,381,128
By employer			1,297,972
Total contributions			5,679,100
Total additions			14,487,186
Deductions from net assets attributed to
Benefits paid to participants			(6,899,961	)
Total deductions			(6,899,961	)
Net increase			7,587,225
Net assets available for benefits
Beginning of year			33,822,651
End of year		$	41,409,876

The accompanying notes are an integral part of these financial statements.

Merck Puerto Rico Employee Savings and Security Plan

1.		Description of the Plan
		The following description of the Merck Puerto Rico Employee Savings and Security Plan (the “Plan”) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan’s provisions.
		General
		The Plan is a profit sharing plan designed to provide an opportunity for employees of Merck Sharp & Dohme Quimica de Puerto Rico, Inc. and Merck Sharp & Dohme (I.A.) Corp. (the “Companies”) to become stockholders of Merck & Co., Inc. (“Merck”) and to encourage them to save on a regular basis by setting aside part of their earnings. Regular full-time and part-time employees of the Companies, as defined in the Plan document, who have completed at least one year of employment and are not covered by a collective bargaining agreement, are eligible to enroll in the Plan.
		The Plan is administered in part by the Employee Benefits Committee appointed by the Presidents of the Companies and in part by a management committee appointed by the Compensation and Benefits Committee of the Board of Directors of Merck. All costs of administering the Plan are borne by the Companies.
		The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 (“ERISA”).
		Contributions
		Participants may contribute from 2% up to 15% of their base pay, provided that pre-tax contributions shall not exceed 10% of base compensation or $8,000. In addition, the Companies match 50% of pre-tax and after-tax contributions up to 5% of each participant’s base compensation applicable to the pay period in which the contribution is being made. Company matching contributions are invested according to a participant’s elections.
		Participants direct the investment of their contributions into any fund investment option available under the Plan, including the Merck Common Stock Fund. During 2006, the Plan offered 16 mutual funds, a commingled fund, a separately managed fund and the Merck Common Stock Fund.
		Participant Accounts
		Each participant’s account is credited with the participant’s contribution, the Companies’ matching contribution, and an allocation of Plan earnings. The allocation is based on participants’ account balances, as defined in the Plan document.
		Vesting
		Participants are immediately vested in their contributions, all Companies’ matching contributions, plus actual earnings thereon.
		Participant Loans
		Participants may borrow from their account balances with interest charged at prime rate plus 1%. Loan terms range from one to five years or up to thirty years for the purchase of a primary residence. The minimum loan is $500 and the maximum loan is the lesser of (i) $50,000 less the highest

Merck Puerto Rico Employee Savings and Security Plan

		outstanding loan balance during the one year period prior to the new loan application date, or (ii) 50% of the participant’s account balance less any current outstanding loan balance.
		Payment of Benefits
		Participants are entitled to receive automatic, voluntary, in-service (which include hardship withdrawals), or mandatory distributions as provided in the applicable Plan provisions.
2.		Summary of Significant Accounting Policies
		Basis of Accounting
		The 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 disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management believes that these estimates are adequate. Actual results could differ from those estimates.
		Investment Valuation and Income Recognition
		The investments of the Plan are stated at quoted market prices in an active market (except for participant loans which are presented at the outstanding balance). Shares of mutual funds are presented at quoted market prices which represent the net asset value of the shares held by the Plan at the reporting date. For the commingled and separately managed funds, the investment units are based on the current market values of the underlying assets of the fund.
		Purchases and sales of securities are recorded on a trade-date basis. Dividend income is recorded on the ex-dividend date. The Plan presents in the statement of changes in net assets available for benefits the net appreciation (depreciation) in the fair value of its investments which consists of the realized gains or losses and the unrealized appreciation (depreciation) on them. Interest income on participant loans is recorded on accrual basis.
		Contributions
		Employee and Companies matching contributions are recorded in the period in which the Companies make the payroll deductions from the participants’ earnings.
		Payment of Benefits
		Benefits are recorded when paid.
		Transfer of Assets to Other Plans
		Companies’ employees or retirees may elect to transfer their savings to other plans qualified by the Puerto Rico Treasury Department (the “PRTD”) or by the U.S. Internal Revenue Service (the “IRS”).

Merck Puerto Rico Employee Savings and Security Plan

		Risks and Uncertainties
		The Plan provides for various investment options in investment securities. Investment securities, in general, are exposed to various risks, such as interest rate, credit 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 statement of net assets available for benefits.
3.		Investments
		The following presents investments that represent 5% or more of the Plan’s net assets as of year-end:

		December 31,
		2006				2005
Merck Common Stock Fund		$	21,289,077			$	15,974,013
Columbia Acorn Fund, Class Z			2,462,764				2,099,540
Fidelity Retirement Money Market Portfolio			2,411,076				2,884,487
T. Rowe Price Blue Chip Growth Fund			2,377,861				2,434,726
American Funds EuroPacific Growth Fund, Class A			2,137,185				1,370,330
Fidelity Low-Priced Stock Fund			1,929,524				1,727,269
		$	32,607,487			$	26,490,365

During 2006, the Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated in value by $7,069,156 as follows:

		Year Ended
		December 31,
		2006
Mutual Funds		$	927,580
Commingled and Separately Managed Funds			297,777
Merck Common Stock Fund			5,843,799
		$	7,069,156

Merck Puerto Rico Employee Savings and Security Plan

4.		Related Party Transactions
		Certain Plan investments are shares of mutual funds managed by Fidelity Management Trust Company (“Fidelity”). Fidelity is the record keeper and custodian as defined by the Plan and, therefore, these transactions qualify as party-in-interest transactions. The total market value of investments in the mutual funds managed by Fidelity was $7,085,691 and $6,307,715 at December 31, 2006 and December 31, 2005, respectively.
		Merck & Co., Inc. also is a party-in-interest to the Plan under the definition provided in Section 3(14) of ERISA. Therefore, Merck Common Stock Fund transactions qualify as party-in-interest transactions. The total market value of investments in the Merck Common Stock Fund was $21,289,077 and $15,974,013 at December 31, 2006 and December 31, 2005, respectively.
5.		Plan Termination
		Although they have not expressed any intent to do so, the Companies have the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions of ERISA. Upon termination of the Plan, each participant thereby affected would receive the entire value of his or her account as though he or she had retired as of the date of such termination.
6.		Tax Status
		The Plan obtained a tax determination letter from the PRTD dated February 18, 1998 indicating that it had been designed in accordance with applicable sections of the Puerto Rico Internal Revenue Code of 1994 (“PRIRC”) and is, therefore, exempt from Puerto Rico income taxes. On August 20, 2003, the Plan obtained a tax determination letter from the Internal Revenue Service indicating it has been designed in accordance with applicable sections of the Internal Revenue Code (“IRC”). However, the Plan has been amended since the receipt of the determination letter. The Plan sponsor and legal counsel believe that the Plan is designed and currently operates in compliance with the PRIRC and IRC. Therefore, no provision for income taxes has been made.
		The Plan failed the non-discrimination test for the year ended December 31, 2006. This failure will be remediated by making additional contributions to non-highly compensated employees in the aggregate amount of $25,724. Considering the remedial actions taken pursuant to the provisions of the Plan Document, management believes that this situation did not affect the tax-exempt status of the Plan.

* * * * *

Supplemental Schedule
Schedule H

Merck Puerto Rico Employee Savings and Security Plan

		Identity of Issuer, Borrower,				Share						Current
		Lessor or Similar Party		Description of Investment		Balance				Cost		Value
*		Merck & Co. Inc.		Merck Common Stock Fund			1,006,825.670			**		$	21,289,077
*		Fidelity Investment Co.		Fidelity Retirement Money Market Portfolio			2,411,076.090			**			2,411,076
				Fidelity Low-Priced Stock Fund			44,316.126			**			1,929,524
				Fidelity Diversified International Fund			41,616.036			**			1,537,713
				Fidelity Freedom 2005 Fund			2,913.117			**			33,821
				Fidelity Freedom 2010 Fund			1,863.468			**			27,244
				Fidelity Freedom 2015 Fund			24,664.742			**			300,910
				Fidelity Freedom 2020 Fund			10,878.874			**			168,949
				Fidelity Freedom 2025 Fund			18,145.852			**			231,723
				Fidelity Freedom 2030 Fund			17,083.370			**			273,846
				Fidelity Freedom 2035 Fund			6,029.196			**			79,525
				Fidelity Freedom 2040 Fund			9,637.149			**			91,360
		T. Rowe Price Associates, Inc.		T. Rowe Price Blue Chip Growth Fund			66,550.817			**			2,377,861
		The Capital Group Companies		American Funds EuroPacific Growth Fund, Class A			45,901.747			**			2,137,185
		Columbia Wanger Asset Management, LP		Columbia Acorn Fund, Class Z			82,893.449			**			2,462,764
		Pacific Investment Management Company		PIMCO Total Return Fund - Institutional Fund			76,854.129			**			797,746
		AXA Rosenberg Investment Management, LLC		AXA Rosenberg U.S. Small Capitalization Fund			84,832.816			**			1,056,327
		SSgA Funds Management, Inc.		SSgA Flagship 500 Index Fund Series A			7,664.007			**			2,059,032
*		Participant Loans		Interest rates ranging from 5% to 10.5% and with maturities through 2034									1,792,543
				Total								$	41,058,226

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the undersigned plan administrator has duly caused this annual report to be signed on behalf of the Merck Puerto Rico Employee Savings and Security Plan by the undersigned hereunto duly authorized.

June 20, 2007

EXHIBIT INDEX

Exhibit
Number		Document		Page
23		Consent of Independent Registered Public Accounting Firm		11