Filed by Amgen Inc. Pursuant to Rule 425
                                                under the Securities Act of 1933
                                        and deemed filed pursuant to Rule 14a-12
                                       under the Securities Exchange Act of 1934

                                           Subject Company:  Immunex Corporation
                                                     Commission File No. 0-12406

This filing relates to the proposed acquisition ("Acquisition") by Amgen Inc.
("Amgen") of Immunex Corporation ("Immunex") pursuant to the terms of an
Agreement and Plan of Merger, dated as of December 16, 2001 (the "Merger
Agreement"), by and among Amgen, AMS Acquisition Inc. and Immunex. The Merger
Agreement is on file with the Securities and Exchange Commission as an exhibit
to the Current Report on Form 8-K, as amended, filed by Amgen today, December
17, 2001, and is incorporated by reference into this filing.

The following is the text of key messages that Amgen has prepared for use in
responding to questions regarding the Acquisition:

For Internal Use Only


 . This is a strategically compelling and unprecedented combination of two of the
  world's fastest growing biotechnology companies, representing a key step in
  Amgen's long-term growth program. It will:
   . Combine most successful biotech company with industry's fastest growing
   . Accelerate Amgen's product sales growth into the low 30s
   . Increase the company's financial strength
   . Further diversify Amgen's product portfolio
   . Establish immediate leadership in inflammation therapy
   . Significantly enhance the company's discovery research capabilities
   . Immediately enhance Amgen's inflammation and oncology pipelines
   . Marry two companies that share a strong cultural fit that is science-based,
     patient-focused, entrepreneurial and hold a biotechnology heritage

 . The transaction gives Amgen, currently the world's leading biotechnology
  company, even greater financial strength to accelerate its long-term growth.
  With Immunex, Amgen will:
   . Have pro forma annual revenues of approximately $5.5 billion and net
     income of $1.5 billion in 2002, assuming an H2 2002 close
   . Have 9,500 employees
   . Generate readily achievable cost synergies of $200 million in 2003 and
     more than $250 million in 2004
   . Benefit from earnings accretion in 2004
   . Accelerate five-year annual percentage growth in product sales to the low
     30s from the low 20s

   . Accelerate annual growth in cash EPS to the mid-20s from the low 20s

 . The combination will have a diverse blockbuster product portfolio,
  unparalleled in the biotechnology world, with no significant patent
  vulnerability until 2013.
   . Immunex brings its proven inflammation blockbuster ENBREL(R) to Amgen's
     existing portfolio including blockbusters EPOGEN(R) and NEUPOGEN(R), and
     potential blockbuster Aranesp(TM). Immunex's ENBREL(R) sales are poised to
     reach over $1 billion in sales in 2002 and $3 billion by 2005
   . Amgen will leverage its substantial development expertise to maximize
     Immunex's pipeline opportunities
   . Amgen will have a rich pipeline, with leadership in three targeted
     therapeutic areas: inflammation, oncology and nephrology, as well as R&D
     focus in proteins, antibodies and small molecules
   . Amgen will be an even more attractive licensing partner

 . With ENBREL(R), a proven blockbuster and the fastest biologic drug ever,
  Amgen will become a leader in inflammation which adds to its leadership in
  nephrology and oncology.
   . With Immunex, Amgen assumes instant market leadership in inflammation.
     ENBREL(R) has first-to-market advantage and tremendous upside potential in
     the robust and growing inflammation market
   . Future growth for ENBREL(R) will be fueled by growth in rheumatoid
     arthritis and other indications, such as psoriatic arthritis
   . Additional market opportunities may exist for the combination ENBREL(R)
     Kineret(TM) therapy aimed at enhancing the well-being of rheumatoid
     arthritis patients
   . The combined company expects to sustain its leadership in inflammation
     through a rich pre-clinical pipeline characterized by innovative and
     differentiated technology.

 . Amgen is the best possible partner for Immunex with experience that can
  help ensure ENBREL(R) achieves its full blockbuster potential.
   . Amgen's experience in bringing successful drugs to market (clinical,
     regulatory, manufacturing, sales and marketing) and optimizing their
     potential makes Amgen an ideal fit for Immunex, with its strength in
     discovery research
   . Amgen is committed to leveraging its protein manufacturing expertise and
     completing Immunex's second ENBREL(R) manufacturing plant in Rhode Island
     to step up production of ENBREL(R) to meet strong market demand
   . Amgen will leverage its inflammation sales force now in place to enhance
     ENBREL(R) sales

 . Amgen is committed to integrating the two companies quickly and to
  maintaining the strong entrepreneurial culture that both companies share.
   . Amgen expects to achieve $200 million in cost synergies in 2003 and more
     than $250 million in 2004, representing approximately 5% of the combined
     company's operating expenses
   . Immunex CEO Ed Fritzky will become a member of Amgen's board
   . Peggy Phillips and Doug Williams from Immunex will assume key roles at
     Amgen by becoming executive vice president and senior vice president,

  . Lower costs from elimination of redundancies, lower M&S expenses and
    leveraging Amgen's strong development and manufacturing capability

 . Amgen is committed to growing its operations over time in Seattle and to
  continuing Immunex's strong tradition of community support.
   . Amgen intends to center its inflammation research in Seattle
   . Amgen has a strong track record of support, partnership and engagement in
     the communities in which it operates

  Additional Information and Where to Find It
  In connection with Amgen's proposed acquisition of Immunex, Amgen and
  Immunex intend to file with the SEC a joint proxy statement/prospectus and
  joint proxy statement/prospectus and other relevant materials (when they
  become available), and any other documents filed by Amgen or Immunex with
  the SEC, may be obtained free of charge at the SEC's web site at In addition, investors and security holders may obtain free
  copies of the documents filed with the SEC by Amgen by directing a request
  to: Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, Attn:
  Investor Relations. Investors and security holders may obtain free copies
  of the documents filed with the SEC by Immunex by contacting Immunex's
  Investor Relations department at 51 University Street, Seattle, WA 98101.
  Investors and security holders are urged to read the joint proxy
  statement/prospectus and the other relevant materials when they become
  available before making any voting or investment decision with respect to
  the acquisition.

  Amgen, Immunex and their respective executive officers and directors may be
  deemed to be participants in the solicitation of proxies from the
  stockholders of Amgen and Immunex in favor of the acquisition. Information
  about the executive officers and directors of Amgen and their ownership of
  Amgen common stock is set forth in the proxy statement for Amgen's 2001
  Annual Meeting of Shareholders, which was filed with the SEC on April 4,
  2001. Information about the executive officers and directors of Immunex and
  their ownership of Immunex common stock is set forth in the proxy statement
  for Immunex's 2001 Annual Meeting of Shareholders, which was filed with the
  SEC on March 16, 2001. Investors and security holders may obtain more
  detailed information regarding the direct and indirect interests of Amgen,
  Immunex and their respective executive officers and directors in the
  acquisition by reading the joint proxy statement/prospectus regarding the
  acquisition when it becomes available.

  Forward-Looking Statements
  This document contains forward-looking statements within the meaning of the
  "safe harbor" provisions of the Private Securities Litigation Reform Act of
  1995, including statements about future financial and operating results and
  Amgen's anticipated acquisition of Immunex. These statements are based on
  management's current expectations and beliefs and are subject to a number
  of risks, uncertainties and assumptions that could cause actual results to
  differ materially from those described in the forward-looking statements.
  All statements other than statements of historical fact are statements that
  could be deemed forward-looking statements. For example, statements of
  expected synergies, accretion, timing of closing, industry ranking,
  execution of integration plans and management and organizational structure
  are all forward-looking statements. Risks, uncertainties and assumptions
  include the possibility that the market for the sale of certain products
  and services may not develop as expected; that development of these
  products and services may not proceed as planned; the Immunex acquisition
  does not close or that the companies may be required to modify aspects of
  the transaction to achieve regulatory approval; that prior to the closing
  of the proposed acquisition, the businesses of the companies suffer due to
  uncertainty; that the parties are unable to successfully execute their
  integration strategies, or achieve planned synergies; and other risks that
  are described in the Securities and Exchange Commission reports filed by
  Amgen, including its most recent Form 10-Q. Amgen conducts research in the
  biotechnology/pharmaceutical field where movement from concept to product
  is uncertain; consequently, there can be no guarantee that any particular
  product candidate will be successful and become a commercial product.

  Furthermore, Amgen's research, testing, pricing, marketing and other
  operations are subject to extensive regulation by domestic and foreign
  government regulatory authorities. In addition, sales of Amgen's products
  are affected by reimbursement policies imposed by third party payors,
  including governments, private insurance plans and managed-care providers.
  These government regulations and reimbursement policies may affect the
  development, usage and pricing of Amgen's products.

  In addition, while Amgen routinely obtains patents for Amgen's products and
  technology, the protection offered by Amgen's patents and patent
  applications may be challenged, invalidated or circumvented by our

  Because forward-looking statements involve risks and uncertainties, actual
  results and events may differ materially from results and events currently
  expected by Amgen and Immunex. Amgen and Immunex assume no obligation and
  expressly disclaim any duty to update information contained in this
  document except as required by law.