UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON D.C. 20549 FORM 11-K (Mark One) [ X ] ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year end December 31, 1999 OR [ ] TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number 000-12477 RETIREMENT AND SAVINGS PLAN FOR AMGEN PUERTO RICO, INC. State Road 31, Kilometer 24.6, Juncos, Puerto Rico 00777 (Full title and address of the plan) AMGEN INC. (Name of issuer of the securities held) One Amgen Center Drive, Thousand Oaks, California 91320-1799 (Address of principal executive offices) (Zip Code)

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Financial Statements and Supplemental Schedule Years ended December 31, 1999 and 1998 Contents Report of Independent Auditors............................................................................... 1 Audited Financial Statements Statements of Net Assets Available for Benefits.............................................................. 2 Statements of Changes in Net Assets Available for Benefits................................................... 3 Notes to Financial Statements................................................................................ 4 Supplemental Schedule Schedule of Assets Held for Investment Purposes at End of Year............................................... 8

Report of Independent Auditors Amgen Puerto Rico, Inc., as Named Fiduciary, and the Plan Participants of the Retirement and Savings Plan for Amgen Puerto Rico, Inc. We have audited the accompanying statements of net assets available for benefits of Retirement and Savings Plan for Amgen Puerto Rico, Inc. (the Plan) at December 31, 1999 and 1998, and the related statements of changes in net assets available for plan benefits for the years then ended. 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 in accordance with auditing standards generally accepted in the 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. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion. In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Plan at December 31, 1999 and 1998, and the changes in its net assets available for benefits for the years then ended in conformity with accounting principles generally accepted in the United States. Our audits were performed for the purpose of expressing an opinion on the financial statements taken as a whole. The accompanying supplemental schedule of assets held for investment purposes at end of year as of December 31, 1999, is presented for purpose of additional analysis and are not a required part of the basic financial statements but are 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. This supplemental schedule has been subjected to the auditing procedures applied in our audit of the 1999 financial statements and, in our opinion, are fairly stated, in all material respects, in relation to the 1999 financial statements taken as a whole. /s/ Ernst & Young LLP April 28, 2000 San Juan, Puerto Rico Stamp No. 1631064 affixed to original of this report. -1-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Statements of Net Assets Available for Benefits December 31 1999 1998 ----------------------------------- Assets Investments at fair value $21,429,514 $11,954,519 Contributions receivable 74,680 52,531 ----------------------------------- Net assets available for benefits $21,504,194 $12,007,050 ==================================== See accompanying notes. -2-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Statements of Changes in Net Assets Available for Benefits Year ended December 31 1999 1998 ------------------------------------ Additions to net assets: Employee contributions $ 1,061,629 $ 842,097 Employer contributions 1,167,733 1,008,770 Rollover contributions 137,422 60,789 Interest and dividend income 698,650 361,931 Realized/unrealized gain 6,957,698 2,975,777 ------------------------------------ Total additions 10,023,132 5,249,364 Deductions from net assets: Benefits paid 522,588 145,078 Fees and commissions 3,400 3,743 ------------------------------------ Total deductions 525,988 148,821 ------------------------------------ Net increase 9,497,144 5,100,543 Net assets available for benefits at beginning of year 12,007,050 6,906,507 ------------------------------------ Net assets available for benefits at end of year $21,504,194 $12,007,050 ==================================== See accompanying notes. -3-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Notes to Financial Statements December 31, 1999 1. Description of the Plan The following description of The Retirement and Savings Plan for Amgen Puerto Rico, Inc. (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 defined contribution plan covering substantially all domestic employees of Amgen Puerto Rico, Inc. (the Company). The Plan was established effective May 1, 1992 and was amended and restated effective April 1, 1996. The Plan is qualified under Section 1165(a) and (e) of the Puerto Rico Income Tax Act of 1954, as amended, and is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA) and Section 401(a) and (k) of the Internal Revenue Code of 1986, as amended (the Code). Contributions The Company makes contributions for all eligible employees, whether or not they have elected to make contributions to the Plan, with a Core contribution equal to 3% of each employee's eligible compensation each pay period. In addition, for employees who make contributions to the Plan, the Company makes matching contributions equal to 100% of the first 5% of the employee's eligible compensation per pay period. Participants may contribute up to 10% of their wages (a maximum of $8,000 and $7,500 in 1999 and 1998, respectively) to the Plan in accordance with the applicable income tax regulations. Such contributions, up to a specified maximum amount, are made on a "pre-tax" basis. Participants select the funds in which their contributions are to be invested, electing among various investment alternatives. Participants may elect for their contributions to be invested in more than one fund; however, no more than 50% of their total contributions may be invested in the Amgen Inc. Stock Fund. Vesting Participants are immediately vested with respect to their individual contributions, and earnings thereon. Participants become vested in the other Company contributions upon completing the requisite number of years of service. Employees must work a minimum of 1,000 hours within a Plan year to receive vesting for that year of service. -4-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Notes to Financial Statements (continued) 1. Description of the Plan (continued) Vesting (continued) The vesting schedule for the Company's matching contributions, and related earnings thereon, is as follows: Years of Service Vesting Percentage ---------------- ------------------ Less than 1 0% 1 but less than 2 25% 2 but less than 3 50% 3 but less than 4 75% 4 or more 100% The vesting schedule for the Company's Core contributions, and related earnings thereon, is as follows: Years of Service Vested Percentage ---------------- ----------------- Less than 5 0% 5 or more 100% The Company's contributions become fully vested upon attainment of normal retirement age, disability or death. Forfeited balances of terminated participants' nonvested accounts are used to reduce future Company contributions. Payment of Benefits Upon retirement, a participant may elect to receive a lump-sum payment in cash and/or shares of the Company's common stock. The number of shares of Company common stock to be paid is based on the quoted market value of such stock on the date the Plan is valued following employee notification. Certain restrictions apply to withdrawals of amounts from the Plan while a participant continues to be employed by the Company. Participant Loans Loans can be made to a participant generally up to 50% of the participant's vested account balance. The loans bear interest at the average borrowing rates of certain major banks (ranging from 8.00% to 9.45% during 1999 and from 8.73% to 12.03% during 1998) and are generally payable in installments over periods ranging from one to five years. Principal and interest payments are allocated to the participant's account. -5-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Notes to Financial Statements (continued) 1. Description of the Plan (continued) Plan Termination Although it has not expressed any intent to do so, the Company has the right under the Plan to terminate the Plan subject to the provisions of ERISA. In the event of termination, participants will become 100% vested in their accounts. Trustee Banco Santander is the trustee of the Plan. 2. Summary of Significant Accounting Policies Basis of Accounting The financial statements have been prepared on the accrual basis of accounting. Reclassification Certain amounts in the 1998 financial statements have been reclassified to conform to the 1999 presentation. Investment Income Dividend income is recognized on the ex-dividend date and interest income is recorded on an accrual basis. Unrealized gains and losses on investments are measured by the change in the difference between the fair value and cost of the securities held at the beginning and end of the period. Realized gains and losses from security transactions are recorded based on the weighted-average cost of securities sold. Investment Valuation Investments in mutual funds and Amgen Inc. common stock are valued at current market values determined through reference to public market information on the last business day of the Plan year. Participant loans are valued at their outstanding balances which approximate fair value. Use of Estimates The preparation of the financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumption that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. -6-

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Notes to Financial Statements (continued) 3. Investments The fair value of individual investments that represent 5% or more of the Plan's net assets is as follows: 1999 1998 ------------------ ------------------ Amgen Inc. Stock Fund $10,085,689 $4,091,643 Fidelity Magellan Fund 2,826,356 1,848,819 Fidelity Spartan U.S. Equity Index 2,238,344 1,713,252 Fidelity OTC Portfolio 1,963,267 935,221 Fidelity Growth & Income Portfolio 1,219,038 969,993 During 1999 and 1998, the Plan's investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated in value by $6,957,698 and $2,975,777 as follows: Year ended 1999 1998 ------------------ ------------------ Amgen Inc. Stock Fund $5,496,131 $1,901,510 Mutual funds 1,461,567 1,074,267 ------------------ ------------------ $6,957,698 $2,975,777 ================== ================== 4. Income Tax Status In April 1996, the Company received a determination letter from the Puerto Rico Treasury Department that the Plan meets the requirements for qualification under the Puerto Rico Income Tax Act and the trust forming a part of the Plan is exempt from income taxes. 5. Services Provided by the Company The Company provides certain administrative and recordkeeping services for the Plan at no cost to the Plan participants. In addition, the Company has paid the trustee fees and other related costs on behalf of the Plan. -7-

Supplemental Schedule

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. EIN: 77-0259777 Plan: 35322 Schedule H, line 4i - Schedule of Assets Held for Investment Purposes at End of Year December 31, 1999 Description of Current Identity of Issue Investment Cost Value - ----------------------------------------------------------------------------------------------------------------------- Amgen Inc.* Common stock 166,056 shares $ 2,332,874 $10,085,689 Fidelity Magellan Fund Mutual fund 20,686 shares 2,146,708 2,826,356 Fidelity Growth & Income Portfolio Mutual fund 25,849 shares 964,557 1,219,038 Fidelity Retirement Money Market Portfolio Money market portfolio 411,279 411,279 Fidelity Overseas Fund Mutual fund 13,612 shares 476,478 653,536 Fidelity Spartan U.S. Equity Index Mutual fund 42,971 shares 1,242,786 2,238,344 Fidelity Short-Term Bond Mutual fund 75,196 shares 651,111 639,168 Fidelity OTC Portfolio Mutual fund 28,884 shares 1,136,208 1,963,267 Fidelity Asset Manager Mutual fund 4,225 shares 74,344 77,651 Fidelity Asset Manager: Growth Mutual fund 15,403 shares 277,727 302,967 Fidelity Asset Manager: Income Mutual fund 9,606 shares 116,001 116,996 Fidelity U.S. Bond Index Portfolio Mutual fund 5,615 shares 60,249 57,213 Fidelity Contrafund Mutual fund 4,357 shares 242,842 261,500 Participant loans* Interest rates from 8% to 9.45% - 576,510 ------------------------------- $10,133,164 $21,429,514 =============================== *Party-in-interest -8-

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized. Retirement and Savings Plan for Amgen Puerto Rico, Inc. (Name of Plan) Date: 6/19/00 By: /s/ Kathryn E. Falberg ------------------------- ---------------------- Kathryn E. Falberg Chief Financial Officer, Amgen Puerto Rico, Inc.

The Retirement and Savings Plan for Amgen Puerto Rico, Inc. Index to Exhibit Consent of Ernst & Young LLP, Independent Auditors Exhibit 1

EXHIBIT 1 Consent of Ernst & Young LLP, Independent Auditors We consent to the incorporation by reference in the Registration Statement (Form S-8 No. 33-47605) pertaining to The Retirement and Savings Plan for Amgen Puerto Rico, Inc. of our report dated April 28, 2000, with respect to the financial statements and supplemental schedule of The Retirement and Savings Plan for Amgen Puerto Rico, Inc. included in this Annual Report (Form 11-K) for the year ended December 31, 1999. /s/ Ernst & Young LLP San Juan, Puerto Rico June 16, 2000