EXHIBIT 5.1

                        [LETTERHEAD OF LATHAM & WATKINS]

                                 March 22, 2002

                                                            FILE NO. 030678-0002

Amgen Inc.
One Amgen Center Drive
Thousand Oaks, California 91320-1799

    Re: Registration Statement on Form S-4 of Common Stock,
        ---------------------------------------------------
        $.0001 par value per share
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Ladies and Gentlemen:

                  In connection with the registration by Amgen Inc., a Delaware
corporation (the "Company"), of 254,517,108 shares of its common stock, par
value $.0001 per share (the "Shares"), under the Securities Act of 1933, as
amended (the "Act"), on Form S-4 filed with the Securities and Exchange
Commission on January 31, 2002, as amended by Amendment No. 1 thereto filed on
March 22, 2002 (the "Registration Statement"), you have requested our opinion
with respect to the matters set forth below.

                  In our capacity as your counsel in connection with such
registration, we are familiar with the proceedings taken and proposed to be
taken by the Company in connection with the authorization, issuance and sale of
the Shares, and for the purposes of this opinion, have assumed such proceedings
will be timely completed in the manner set forth in the Amended and Restated
Agreement and Plan of Merger by and among the Company, AMS Acquisition Inc. and
Immunex Corporation, dated as of December 16, 2001 (the "Merger Agreement"). In
addition, we have made such legal and factual examinations and inquiries,
including an examination of originals or copies certified or otherwise
identified to our satisfaction of such documents, corporate records and
instruments, as we have deemed necessary or appropriate for purposes of this
opinion.

                  In our examination, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals, and
the conformity to authentic original documents of all documents submitted to us
as copies.

                  We are opining herein as to the effect on the subject
transaction only of the General Corporation Law of the State of Delaware, and we
express no opinion with respect to the applicability thereto, or the effect
thereon, of the laws of any other jurisdiction or, in the case of Delaware, any
other laws, or as to any matters of municipal law or the laws of any local
agencies within any state.

                  In rendering this opinion, we have assumed that prior to the
issuance of any of the Shares (i) the Registration Statement will have become
effective under the Act, (ii) the



LATHAM & WATKINS
Amgen Inc.
March 22, 2002
Page 2


stockholders of the Company will have approved the issuance of the Shares,
(iii) the shareholders of Immunex Corporation will have approved the Merger
Agreement, and (iv) the transactions contemplated by the Merger Agreement
are consummated in accordance with the Merger Agreement.

                  Subject to the foregoing, it is our opinion that the Shares
have been duly authorized, and, upon issuance, delivery and payment therefor in
the manner contemplated by the Merger Agreement, will be validly issued, fully
paid and nonassessable.

                  We consent to your filing this opinion as an exhibit to the
Registration Statement and to the reference to our firm contained under the
heading "Legal Matters."

                                 Very truly yours,

                                 /s/ Latham & Watkins