Contact:  Sheryl Williams (media)
          610-738-6493
          Sandra Menta (investors)
          610-738-6376

FOR IMMEDIATE RELEASE
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     Cephalon Announces Early Payment of $30 Million Revenue-Sharing Notes

     West Chester, PA -- December 30, 1999 -- Cephalon, Inc. (NASDAQ: CEPH)
today announced that it has agreed to accelerate the maturity of the revenue-
sharing notes that were initially offered in a private sale in February 1999.
The notes will now mature during the first quarter of 2000, and will be retired
for an aggregate cash payment of $35.5 million. Under the original terms of the
notes, the company was to pay $30 million in cash for the notes in
February 2002.

     Early payment of the notes shortens by two years the period during which
noteholders are eligible to receive royalties on U.S. sales of PROVIGIL(R)
(modafinil) Tablets [C-IV]. Investors will retain the Class B Warrants, which
were issued in connection with the original offering of the notes, to purchase
480,000 shares of Cephalon common stock; the investors have the option to
immediately exercise the warrants. The company will recognize a fourth quarter
charge to earnings of approximately $11 million representing the payment
premium, and unamortized debt discount and other costs recorded upon original
issuance of the notes. The noteholders of the offering are The Kauffman Fund,
Sprout Group and Delta Opportunity Fund.

     Cephalon, Inc., headquartered in West Chester, Pennsylvania, is an
international biopharmaceutical company dedicated to the discovery, development
and marketing of products to treat neurological disorders, sleep disorders and
cancer.

     In addition to historical facts or statements of current condition, this
press release may contain forward-looking statements. Forward-looking statements
provide Cephalon's current expectations or forecasts of future events. These may
include statements regarding anticipated scientific progress on its research
programs, development of potential pharmaceutical products, prospects for
regulatory approval, manufacturing development and capabilities, market
prospects for its products, sales and earnings projections, and other statements
regarding matters that are not historical facts. You may identify some of these
forward-looking statements by the use of words in the statements such as
"anticipate," "estimate," "expect," "project," "intend," "plan," "believe" or
other words and terms of similar meaning. Cephalon's performance and financial
results could differ materially from those reflected in these forward-looking
statements due to general financial, economic, regulatory and political
conditions affecting the biotechnology and pharmaceutical industries as well as
more specific risks and uncertainties such as those set forth below and in its
reports on Form 8-K, 10-Q and 10-K filed with the U.S. Securities and Exchange
Commission. Given these risks and uncertainties, any or all of these
forward-looking statements may prove to be incorrect. Therefore, you are
cautioned not to place too much reliance on any such factors or forward-looking
statements. Furthermore, Cephalon does not intend (and it is not obligated) to
update publicly any forward-looking statements, whether as a result of new
information, future events or otherwise. This discussion is permitted by the
Private Securities Litigation Reform Act of 1995.

     NOTE: Cephalon's press releases are posted on the Internet at the company's
Web site at http://www.cephalon.com. They are also available by fax 24 hours a
day at no charge by calling PR Newswire's Company News On-Call at 800-758-5804,
extension 134563.