"PHASE III TRIAL OF ORAL CLADRIBINE......[CLICK HERE FOR: TheCLARITYStudy.com]

A NOVEL INVESTIGATIONAL THERAPY FOR MULTIPLE SCLEROSIS,
BEGINS IN THE UNITED STATES

Nationwide Recruitment Begins at Sites Across the U.S.

Rockland, Massachusetts, and Geneva, Switzerland, May 4, 2006 - Serono (virt-x: SEO and
NYSE: SRA) announced today that recruitment in the U.S. is beginning for the Phase III
CLARITY study (CLAdRIbine Tablets in Treating MS OrallY Study) of oral cladribine for the
treatment of patients with relapsing forms of multiple sclerosis (MS). This multi-national study
was successfully initiated outside the U.S. in 2005, and will now expand to include 17 clinical
trial sites in the U.S. The study is one of the largest MS trials ever conducted, and enrollment is
on track to be completed in 2006.

CLARITY is a two-year, double-blind, placebo-controlled Phase III study of more than 1,200
patients. It is designed to assess patients’ clinical relapses, disability progression and MRI
(magnetic resonance imaging) brain activity. Previous clinical trials using cladribine
administered by injection in patients with MS showed positive effects in reduction of new lesion
development in the brain as seen on MRI scans; reductions in relapses were also observed.

“The Phase III CLARITY trial is enrolling at a strong pace, and the addition of US sites will
accelerate this pace and bring us one step closer to our goal of making the first oral MS therapy
available for people living with this debilitating condition, underscoring our fundamental and
long-term commitment to the MS community,” said Dr. Paul Lammers, Chief Medical Officer at
Serono, Inc. “The formulation of oral cladribine, combined with the proposed short dosing
regimen, should help patients to be more compliant with their MS therapy and lighten the
patient’s treatment burden associated with chronic MS.”

“We all are looking forward to the day when there is an FDA approved oral therapy that can
affect the underlying disease process in MS,” said Dr. John Richert vice president research and
clinical programs at the National MS Society. “Clinical studies, such as CLARITY, are an
important part of the process leading to the development of these new medications. Those
interested in determining whether they are eligible to participate in the clinical trial should speak
with their healthcare provider.”

Trial Recruitment Taking Place in 15 States
Currently, there are 17 clinics, medical centers, universities and hospitals recruiting patients to
participate in the study in 15 major cities across the country, including:

• Medford, OR • Ann Arbor, MI
• Newark, NJ • Oklahoma City, OK
• Boulder, CO • Charleston, SC
• Las Vegas, NV • Columbus, OH
• Fort Wayne, IN • Chicago, IL
• Durham, NC • Edmonds, WA
• Baltimore, MD • Atlanta, GA
• Charleston, WV

Further clinical trail site information is available at www., or the U.S.
National Institutes of Health clinical trial information website at www.ClinicalTrials.gov.

“We are excited to further evaluate oral cladribine for the treatment of MS,” said Dr. Dusan
Stefoski, M.D., associate professor of the Rush Multiple Sclerosis Center and a clinical
investigator for the CLARITY trial. “From my clinical experience, the addition of an oral therapy
for MS could improve compliance among patients and potentially change the MS treatment
paradigm.”

It is estimated that approximately 400,000 Americans are affected with MS, a chronic,
progressive autoimmune disease of the central nervous system (CNS). Relapsing forms of MS
are the most common. While symptoms of MS are unpredictable and can vary, the most
common symptoms of MS include blurred vision, numbness or tingling in the limbs and
problems with strength and coordination.

About Oral Cladribine
Oral cladribine is a proprietary oral tablet formulation of cladribine that is being studied in an
effort to demonstrate possible benefits as a treatment for patients with relapsing forms of MS.
Cladribine is a purine nucleoside analogue 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, cladribine tablets may offer an
effective new option to patients with MS....."