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

                                          Subject Company:  Immunex Corporation
                                                  Commission File No. 000-12406


         The following is a joint press release issued by Amgen Inc. and
Immunex Corporation in connection with the acquisition of Immunex
Corporation by Amgen Inc. pursuant to an Agreement and Plan of Merger,
dated as of December 16, 2001, by and among Amgen Inc., AMS Acquisition
Inc. and Immunex Corporation.

Amgen to Acquire Immunex for $16 Billion in Stock and Net Cash

12/17/2001

THOUSAND OAKS, Calif. and SEATTLE, Dec. 17, 2001


         -- Combines Two of the World's Fastest Growing Biotechnology Leaders

         -- Creates Unparalleled Portfolio of Blockbuster Biotechnology Drugs
with ENBREL(R), EPOGEN(R), NEUPOGEN(R)and Aranesp(TM)

         -- Amgen Adds Premier Inflammation Franchise to Leadership Position
in Nephrology and Oncology

         -- Amgen Will Have Approximately $5.5 Billion in Pro Forma Annual
Revenues and More Than $1.5 Billion in Net Income in 2002

         -- Acquisition of Immunex Will Increase Amgen's Long-term Product
Sales Growth Rate to Low 30s and Cash EPS Growth Rate to Mid-20s Driven By
Potential ENBREL(R) Sales of $3 Billion or More by 2005

         -- Expected Dilution of Less Than Five Percent in 2003; Accretive
in 2004 and Beyond, on a Cash EPS Basis

         Amgen (Nasdaq: AMGN) and Immunex Corporation (Nasdaq: IMNX)
jointly announced today they have signed a definitive agreement providing
for Amgen, the world's largest biotechnology company, to acquire Immunex,
biotechnology's inflammation leader, for $16 billion in stock and net cash.
Under the terms of the agreement, each share of Immunex common stock will
be exchanged for a fixed-ratio of 0.44 shares of Amgen common stock, and
cash of $4.50, or a total of 85% in stock and 15% in cash.

         The acquisition will bring together two of the world's fastest
growing biotechnology companies, representing a key step in accelerating
Amgen's long-term growth. By combining the most successful biotech company
with one of the industry's fastest growing players, the transaction will
enhance Amgen's position as the biotechnology leader with an unparalleled
portfolio of blockbuster drugs. Proven blockbusters include Amgen's
EPOGEN(R) and NEUPOGEN(R), and Immunex's ENBREL(R). In addition, Amgen's
Aranesp(TM), a recently marketed product, has blockbuster potential.

         With the acquisition, Amgen expects to accelerate its five-year
annual percentage growth in product sales to the low 30s from the low 20s,
and accelerate its annual growth in cash EPS to the mid-20s from the low
20s. Amgen will have pro forma 2002 revenues of approximately $5.5 billion
and 2002 net income in excess of $1.5 billion. This transaction will be
dilutive in 2003 at less than 5%, and is expected to be accretive in 2004,
on a cash EPS basis. Estimated cost synergies are expected to total more
than $200 million in 2003, and more than $250 million in 2004, representing
approximately 5% of the combined company's operating expenses.

         "This is a compelling strategic transaction and an excellent
opportunity for the shareholders, employees and partners of both companies,
and we expect it will generate significant benefits for hundreds of
thousands of patients around the world," said Kevin Sharer, Chairman and
Chief Executive Officer of Amgen. "We firmly believe that, as a result of
this combination, ENBREL(R) -- the fastest growing biologic drug ever --
will reach its peak of $3 billion or more in annual sales. Accordingly,
this acquisition will make Amgen a leader in the more than $10 billion
potential inflammation market in biologics. The balance of safety,
efficacy, and dosing of ENBREL(R), as well as the extension of applications
for the treatment of psoriasis and psoriatic arthritis have potential to
lead to even further commercial success. Overall, the combination will
increase our financial strength, further diversify our product portfolio
and accelerate our long-term growth."

         Sharer continued, "We are strongly committed to growing Immunex's
world-class discovery research capabilities, and we look forward to working
closely with the impressive team they have built by concentrating
inflammation research in Seattle. We plan to move forward in Seattle with
the Helix Project to consolidate existing multiple sites into one
location."

         "Amgen's experience in bringing successful drugs to market and
maximizing their therapeutic and commercial benefits will ensure that
ENBREL(R) achieves its full blockbuster potential. Immunex's recognized
research excellence in immunology and inflammation will benefit our
discovery research programs," said Sharer. "We intend to apply our
significant resources and expertise in protein manufacturing to step up
production and distribution of ENBREL(R) to meet strong market demand. The
first manufacturing facility in Rhode Island is completed, and we are
committed to completing construction of the second plant to help meet that
demand."

         "Together, we will be the leader in meeting the needs of
rheumatoid arthritis patients, and we also plan to continue exploring
potential combination therapies to treat inflammation," said Sharer.

         He concluded: "This is a perfect strategic fit, and we are
confident that we can achieve a rapid and organized integration. The
entrepreneurial spirit and speed with which we operate will continue to
define our science-based, patient-focused company."

         Ed Fritzky, Chairman and Chief Executive of Immunex, who will join
the Amgen board of directors, said: "It is a superb transaction for our
shareholders. By accelerating our strategic and financial plan, this
transaction creates a tremendous opportunity for Immunex shareholders to
participate in the clear potential of this biotech powerhouse. Amgen
clearly values our discovery research capabilities, including excellence in
inflammation, immunology, oncology, and vascular biology, and intends to
build on what we have created. The strength of this combination lies in
expanding future patient benefits by harnessing the significant resources,
talents and assets of these two leading organizations."

         "In addition, Peggy Phillips and Doug Williams will continue to
play significant roles in the new company by becoming Executive Vice
President, and Senior Vice President, respectively. Both will join Amgen's
executive committee. Phillips will report to Kevin Sharer, and Williams to
Roger Perlmutter, Executive Vice President, Research & Development," he
concluded.

         Transaction Terms

         Under the terms of the agreement, each share of Immunex common
stock will be exchanged for a fixed-ratio of 0.44 shares of Amgen common
stock and cash of $4.50, or a total of 85% in stock and 15% in cash. Amgen
will acquire Immunex in a tax-free reorganization, and the Immunex
shareholders will not be taxed to the extent that they exchange their
Immunex stock for Amgen stock. Amgen's existing shareholders will own
approximately 81% of the new company and Immunex's existing shareholders
will own 19%. As part of the agreement, Amgen will acquire the 41% stake in
Immunex held by American Home Products Corporation (NYSE: AHP), for the
same purchase price per share, giving AHP an 8% stake in the new company.
AHP has agreed to vote in favor of the transaction. The transaction is
anticipated to close in the second half of 2002, subject to approval by
shareholders of both companies, as well as customary regulatory approvals.

         Robert Essner, President and Chief Executive Officer of AHP, said:
"We are very pleased with today's announcement by Amgen and Immunex. Amgen
shares our belief in the huge potential of ENBREL(R) in the robust and
growing inflammation market. As everyone knows, ENBREL(R) has
first-to-market advantage and tremendous upside potential. AHP believes
that the combination of these two companies will create a dynamic and
powerful leader in the biotechnology industry. The fine relationship we
have enjoyed with Immunex over the past several years in the launch and
co-promotion of ENBREL(R) will be enhanced by the excellent biologics
manufacturing capability, sales force and other resources that Amgen will
bring to the partnership."

         Strategic Pipeline

         With the acquisition of Immunex, Amgen will enhance its existing
new drug pipeline in oncology and inflammation. In its existing oncology
pipeline, Amgen holds pegfilgrastim, a long-acting version of its
blockbuster NEUPOGEN(R), a white blood cell booster; Aranesp(TM), for the
treatment of anemia in certain types of chemotherapy; epratuzumab, a novel
cancer therapeutic antibody for non-Hodgkin's lymphoma; and, KGF, or
keratinocyte growth factor, to treat oral mucositis in cancer patients.
This acquisition will add ABX-EGF, a fully human antibody currently being
studied in collaboration with Abgenix in certain advanced cancers; and a
number of pre-clinical candidates.

         In inflammation, ENBREL(R) has been the leading biologic for the
treatment of rheumatoid arthritis since its launch in 1998. It is under
review at the U.S. Food and Drug Administration for a new indication in
psoriatic arthritis, phase 3 studies are under way in severe psoriasis and
phase 2 studies in ankylosing spondylitis. Amgen has recently launched the
first IL-1 inhibitor, Kineret(TM), which is used to treat the signs and
symptoms of rheumatoid arthritis. In addition, Amgen's sTNF-RI product
candidate is being investigated in slowing the markers of disease
progression in rheumatoid arthritis; and inhibitors of OPG/OPGL signaling
have been shown to inhibit bone destruction in clinical studies. Immunex
has also initiated phase 1 studies of the IL-1 receptor type II in
rheumatoid arthritis and is developing other candidates as well.

         Webcast/Teleconference Information

         A conference call and webcast will be held for the investment
community on Monday, December 17, 2001, at 9:00 a.m.EST/6:00 a.m. PST. The
dial-in number for domestic callers is (877) 817-2450. The dial-in number
for international callers is (706) 634-7548. A replay of the call will be
available for 30 days beginning approximately four hours after the call's
conclusion. The replay number for domestic callers is (800) 642-1687, using
the passcode 271-2097. The replay number for international callers is (706)
645-9291, also using the passcode 271-2097. Live audio of the conference
call will be simultaneously broadcast over the Internet and will be
available to members of the news media, investors and the general public.
Access to live and replay audio of the conference call will be available by
following the appropriate links at http://amgen.acquisitioninformation.com.
The event will be archived and available for replay for 30 days beginning
approximately four hours after the call's conclusion.

         About Immunex

         Immunex Corporation is a leading biopharmaceutical company
dedicated to improving lives through immune system science innovation. The
company has received numerous awards for both its scientific achievements
and its overall workplace environment since its inception in 1981. Immunex
is an innovator in the biopharmaceutical industry, and is responsible for
the production of the world's fastest growing biotechnology product,
ENBREL(R), used to treat rheumatoid arthritis. The company recently broke
ground in Rhode Island and began construction of a new, large-scale
manufacturing facility to help ensure the long-term supply of ENBREL(R).

         About Amgen

         Amgen is a leading global biotechnology company that discovers,
develops, manufactures and markets important human therapeutics based on
advances in cellular and molecular biology. Founded in 1980 with a staff of
seven, Amgen has grown into a global corporation with more than 7,000
employees worldwide. As the world's largest biotechnology company, Amgen
discovered and markets the two most successful biotechnology products --
EPOGEN(R), which treats anemia, and NEUPOGEN(R), which fights infection in
cancer chemotherapy patients. In the past two months, Amgen launched
Aranesp(TM), which requires fewer injections than current anemia therapy,
and Kineret(TM), for the reduction in signs and symptoms of rheumatoid
arthritis.

         About AHP

         American Home Products Corporation is one of the world's largest
research-based pharmaceutical and health care products companies. It is a
leader in the discovery, development, manufacturing and marketing of
prescription drugs and over-the-counter medications. It is also a leader in
vaccines, biotechnology, and animal health care.

         Forward-Looking Statements

         This news release 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 and Immunex, including their most recent filings on
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
competitors.

         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 news release except as required by law.

         Additional Information About the Acquisition 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 other relevant materials. INVESTORS AND SECURITY HOLDERS OF AMGEN AND
IMMUNEX ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND THE
OTHER RELEVANT MATERIALS WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL
CONTAIN IMPORTANT INFORMATION ABOUT AMGEN, IMMUNEX AND THE ACQUISITION. The
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
www.sec.gov. In addition, investors and security holders may obtain free
copies of the documents (when they are available) 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 Investor Relations at 51 University St.,
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.


         EDITOR'S NOTE: An electronic version of this news release will be
available via the Amgen and Immunex Web sites, at www.amgen.com and
www.immunex.com, respectively.


         CONTACT: Amgen
Jeff Richardson, 805-447-3227 (media)
Cary Rosansky, 805-447-4634 (investors)
or
                  Immunex
Robin Shapiro, 206-389-4040 (media)
Mark Leahy, 206-389-4363 (investors)
or
                  AHP
Lowell Weiner, 973-660-5013 (media)
Justin Victoria, 973-660-5340 (investors)

04:47 EST DECEMBER 17, 2001