Oral Cladribine on Track to Become First Oral Disease Modifying Treatment
                           for Multiple Sclerosis

    GENEVA, Switzerland, January 16 /PRNewswire-FirstCall/ -- Merck Serono
(virt-x: SEO and NYSE: SRA) announced today that patient enrollment has
been completed in the CLARITY (CLAdRIbine Tablets Treating MS OrallY)
study, a Phase III pivotal clinical trial evaluating the efficacy and
safety of Merck Serono's proprietary oral formulation of cladribine for the
treatment of relapsing forms of multiple sclerosis (MS).
    "The completion of patient enrollment into the CLARITY pivotal trial is
a major milestone in the development program of oral cladribine," said
Franck Latrille, Merck Serono's Head of Product Development. "It brings us
one step closer to our objective of offering patients the first oral
therapy for first line treatment of multiple sclerosis, with the
convenience of short courses of therapy given intermittently."
    The CLARITY study is a two-year (96 weeks), randomized, double-blind,
placebo-controlled, international trial. It enrolled more than 1,300
patients and will provide data on key endpoints including clinical
relapses, disability progression and magnetic resonance imaging (MRI).
Study participants have been enrolled in one of the three arms of the study
to receive one of two different dose regimens of oral cladribine or
matching placebo tablets. In the study, oral cladribine is given in two or
four treatment cycles in the first year, with each cycle consisting of
daily administration for five consecutive days, which means study patients
take oral cladribine therapy for only 10 or 20 days during the year. In the
second year, two treatment cycles are administered.
    The increased convenience resulting from the oral intermittent
administration of oral cladribine has the potential to address an important
unmet medical need in patients with MS.
    Oral cladribine was designated a Fast Track product by the US Food and
Drug Administration (FDA) in September 2006. Under Fast Track designation,
oral cladribine is eligible for Priority Review and the FDA may consider
portions of the marketing application for review before the New Drug
Application (NDA) is completed.
    About oral cladribine
    Merck Serono's proprietary oral formulation of cladribine is currently
being evaluated in Phase III as a treatment for patients with relapsing
forms of multiple sclerosis (MS). Cladribine is a small molecule that
interferes with the behavior and the proliferation of certain white blood
cells, particularly lymphocytes, which are involved in the pathological
process of MS. Through its differentiated mechanism of action, oral
cladribine may offer a safe and effective new option to patients with MS.
    About Merck Serono and multiple sclerosis
    Merck Serono is a leader in multiple sclerosis (MS) with Rebif(R)
(interferon beta-1a), a disease-modifying drug used to treat relapsing
forms of MS, which is registered in more than 80 countries worldwide. In
addition to Rebif(R), the Company also offers a second therapy within its
US portfolio of MS therapies: Novantrone(R) (mitoxantrone for injection
concentrate) for worsening forms of MS. Full prescribing information for
these products can be obtained by contacting the Company or visiting its
website. Additional therapeutic options are currently under development at
Merck Serono, including oral cladribine, currently in Phase III and
potentially the first oral therapy for MS, as well as several products in
early stage development including: osteopontin, an MMP-12 inhibitor, a JNK
inhibitor and interferon beta:Fc. Merck Serono also is taking a leading
role in developing an understanding of the role of genetics in MS, with a
whole genome scan currently underway.
    About multiple sclerosis
    Multiple sclerosis (MS) is a chronic, inflammatory condition of the
nervous system and is the most common, non-traumatic, neurological disease
in young adults. The World Health Organization estimates that up to 2.5
million people suffer from MS worldwide. While symptoms can vary, the most
common symptoms of MS include blurred vision, numbness or tingling in the
limbs and problems with strength and coordination. The relapsing forms of
MS are the most common.
    Forward-looking statements
    Some of the statements in this press release are forward looking. Such
statements are inherently subject to known and unknown risks, uncertainties
and other factors that may cause actual results, performance or
achievements of Merck Serono S.A. and affiliates to be materially different
from those expected or anticipated in the forward-looking statements.
Forward-looking statements are based on Merck Serono's current expectations
and assumptions, which may be affected by a number of factors, including
those discussed in this press release and more fully described in Serono's
Annual Report on Form 20-F filed with the U.S. Securities and Exchange
Commission on February 28, 2006. These factors include any failure or delay
in Merck Serono's ability to develop new products, any failure to receive
anticipated regulatory approvals, any problems in commercializing current
products as a result of competition or other factors, our ability to obtain
reimbursement coverage for our products, the outcome of any government
investigations and litigation. Merck Serono is providing this information
as of the date of this press release, and has no responsibility to update
the forward-looking statements contained in this press release to reflect
events or circumstances occurring after the date of this press release.
    About Merck Serono
    Merck Serono is a global biotechnology leader, with sales in over 90
countries. The Company is the world leader in reproductive health, with
Gonal-f(R), Luveris(R) and Ovidrel(R)/Ovitrelle(R). It has strong market
positions in neurology, with Rebif(R), as well as in metabolism and growth,
with Saizen(R), Serostim(R) and Zorbtive(TM). The Company has recently
entered the psoriasis area with Raptiva(R). Merck Serono's research
programs are focused on growing these businesses and on establishing new
therapeutic areas, including oncology and autoimmune diseases.
    Bearer shares of Merck Serono S.A., the holding company, are traded on
the virt-x (SEO) and its American Depositary Shares are traded on the New
York Stock Exchange (SRA).
    About Merck
    Merck is a global pharmaceutical and chemical company with sales of EUR
5.9 billion in 2005, a history that began in 1668, and a future shaped by
about 35,000 employees (including Merck Serono) in 56 countries. Its
success is characterized by innovations from entrepreneurial employees.
Merck's operating activities come under the umbrella of Merck KGaA, in
which the Merck family holds a 73% interest and free shareholders own the
remaining 27%. In 1917 the U.S. subsidiary Merck & Co. was expropriated and
has been an independent company ever since.

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