Exhibit 5.1


                [ORRICK, HERRINGTON & SUTCLIFFE LLP LETTERHEAD]


                                November 9, 2000


Immunex Corporation
51 University Street
Seattle, WA  98101

Ladies and Gentlemen:

     We are counsel to Immunex Corporation, a Washington corporation (the
"Company"). We have acted as counsel to the Company in connection with the sale
by certain selling shareholders of the Company (the "Selling Shareholders") of
up to 10,000,000 shares (the "Shareholder Firm Shares") of the Company's common
stock, $.01 par value per share (the "Common Stock"), together with an
additional 1,500,000 shares of Common Stock if and to the extent the
underwriters exercise an over-allotment option granted by the Selling
Shareholders (the "Option Shares"), and in connection with the preparation and
filing of a registration statement on Form S-3 (the "Registration Statement")
pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the
"Securities Act"), with respect to the Shareholder Firm Shares and the Option
Shares.

     We have examined the Registration Statement and such instruments, documents
and records which we have deemed necessary for the purpose of this opinion.
Based upon the foregoing, we are of the opinion that upon the happening of the
following events:

     (a)  the effectiveness of the Registration Statement and any amendments
          thereto;

     (b)  due action by the Selling Shareholders authorizing the sale of the
          Shareholder Firm Shares and the Option Shares;

     (c)  the offering and sale of the Shareholder Firm Shares and, to the
          extent the underwriters exercise the over-allotment option, the Option
          Shares, as contemplated by the Registration Statement and the
          Underwriting Agreement and in accordance with the Shareholder actions
          authorizing the sale of Shareholder Firm Shares and Option Shares; and

     (d)  receipt by the Selling Shareholders of the consideration for the
          Shareholder Firm Shares and, to the extent the underwriters exercise
          their over-allotment option, for the Option Shares, as contemplated by
          the Registration Statement and the Underwriting Agreement;


the Shareholder Firm Shares and, to the extent the underwriters exercise their
over-allotment option, the Option Shares, will be duly authorized, validly
issued, fully paid and nonassessable.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and any amendment thereto, including any and all post-
effective amendments, and to the reference to our firm in the prospectus of the
Registration Statement under the heading "Legal Matters." In giving this
consent, we do not thereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act.


                              Very truly yours,

                              /s/ Orrick, Herrington & Sutcliffe LLP