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                                                          Exhibit 10.23


                                FOURTH AMENDMENT
                                       TO
                     REAL ESTATE PURCHASE AND SALE AGREEMENT

     THIS FOURTH AMENDMENT TO REAL ESTATE PURCHASE AND SALE AGREEMENT 
("Amendment") is made and entered into as December 1, 1997, by and between 
THE PORT OF SEATTLE, a Washington special purpose municipal corporation 
("Seller"), and IMMUNEX CORPORATION, a Washington corporation (.Buyer.).

                                    RECITALS

          A. Seller and Buyer entered into a Real Estate Purchase and Sale 
Agreement dated as of July 18, 1994, which was amended by First Amendment to 
Real Estate Purchase and Sale Agreement dated April 7, 1995 and Second 
Amendment to Real Estate Purchase and Sale Agreement dated June 1, 1996 and 
Third Amendment to Real Estate Purchase and Sale Agreement dated January 31, 
1997 (as amended, "Agreement".), pursuant to which Seller agreed to sell and 
Buyer agreed to buy approximately 29 acres of real property known as Terminal 
88, as more particularly described on EXHIBIT A to the Agreement 
("Property"). All capitalized terms not defined herein shall have the 
meanings given them in the Agreement.

          B. Seller and Buyer desire to amend the Agreement as set forth in 
this Amendment.

                                    AGREEMENT

          IN CONSIDERATION of the respective agreements hereinafter set 
forth, Seller and Buyer agree as follows:

          1. CLOSING DATE. Seller and Buyer acknowledge that, as of the date 
hereof, Buyer's Contingencies set forth in Sections 4.3(g)-(h) of the 
Agreement (among others) have not been satisfied. The "Closing Date" shall be 
extended to March 31, 1998, or such other date prior thereto as Seller and 
Buyer may agree to in writing, provided that all of Contingencies and 
Seller's Contingencies have then been either satisfied or waived in 
accordance with Sections 4.3-4.6 of the Agreement. Seller acknowledges that 
Buyer's Contingencies set forth in Sections 4.3(b), (c), (d), (e) and (f) 
have been satisfied and that the City of Seattle  Director of the Department 
of Construction and Land Use will issue to Buyer the Master Use Permit for 
the Project on the Closing Date.

          2. EFFECT OF AMENDMENT. Except as forth in this Amendment, all of 
the terms of the Agreement are hereby ratified and confirmed and shall remain 
in full force and effect.


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         IN WITNESS WHEREOF,  the parties hereto have executed this Amendment as
of the date first above written.

    SELLER:                         THE PORT OF SEATTLE, a limited purpose
                                    municipal corporation


                                    By  /s/  Maud Daudon
                                    Name  Maud Daudon
                                    Title  Chief Financial Officer



    BUYER:                          IMMUNEX CORPORATION, a
                                    Washington corporation


                                    By  /s/  D. G. Southern
                                    Name  D. G. Southern
                                    Title  Senior Vice President


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