Relapses

The primary endpoint of the study is a comparison of the proportion of relapse-free patients after 24 weeks expressed as an odds ratio. 25.1% of patients treated with Rebif(R) experienced a relapse during six months of treatment compared with 36.7% on Avonex(R), a relative difference of 32%. The adjusted odds ratio of relapse-free patients was 1.9 meaning that patients treated with Rebif(R) had 90% greater odds of remaining relapse-free relative to patients treated with Avonex(R). This result is highly statistically significant with a p value of 0.0005.

The average number of relapses during 6 months for patients treated with Rebif(R) was 0.29 and for those treated with Avonex(R) was 0.40, a relative reduction of 27% in favor of Rebif(R) (p value 0.022).

The relative risk of experiencing a relapse at any time within 6 months was 37% less for Rebif(R) patients relative to Avonex(R) patients (p value 0.001).

The need for steroids to treat relapses for the Rebif(R) group was 47% less, relative to the Avonex(R) group (p value 0.004).

MRI disease activity

The main secondary endpoint is the difference in combined unique lesion activity as measured by monthly MRI brain scans over 6 months. On average, patients treated with Avonex(R) had 50% more new lesions in the brain relative to those treated with Rebif(R). Rebif(R) treated patients had an average of 0.8 lesions per scan while Avonex(R) patients had an average of 1.2 lesions per scan. This result is highly statistically significant with a p value of less than 0.0001.

The proportion of brain scans per patient showing disease activity in the Rebif(R) group was 24.0% compared with 37.3% in the Avonex(R) group, a statistically significant reduction in favor of Rebif(R) (p value of less than 0.001).

The proportion of patients with no new disease activity, as measured by MRI, was 48.3% in the Rebif(R) group compared with 33.2% in the Avonex(R) group, a statistically significant difference in favor of Rebif(R) (p value of less than 0.001).

Safety and tolerability

Overall, 97% of patients completed 24 weeks on study with no statistically significant difference in withdrawal rates between the groups. Both formulations of IFN beta-1a were generally well tolerated. Although there were more injection site reactions and elevated liver enzymes associated with the higher and more frequent doses of Rebif(R) used, these were usually mild in nature. There were no cases of injection site necrosis with either medication.

Rebif(R)

Rebif(R) is registered in 67 countries worldwide and is currently the fastest growing treatment for MS outside the USA. In 2000, Rebif(R) achieved worldwide sales of $254.2m.

Conference Call and Webcast

Serono will hold a conference call today, June 22, 2001, at 4:30 P.M. Central European Time (3:30 P.M. London Time, 10:30 A.M. Eastern Daylight Time) during which Serono Management will present the outcome of the EVIDENCE study. To join the telephone conference please dial (+41.91.610.41.11 from Europe) and (+1.412.858.46.00 from the U.S.). The event will be relayed by live audio webcast (listen only mode) which interested parties may access via Serono's corporate home page www.serono.com . A series of slides will be available via the website at 14:00 CET.

A link to the webcast will be provided immediately prior to the event. Additionally, the webcast will be available for replay until close of business on 20th July 2001. The telephone play back will be available until 27th June 2001 using the following numbers and a PIN code of 320#: (+41.91.610.25.00 from Europe) and (+1.412.858.14.40 from the U.S.).

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 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 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 April 23, 2001. These factors include any failure or delay in 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, and government regulations limiting our ability to sell our products. Serono 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 Serono

Serono is a global biotechnology leader. The Company has six recombinant products on the market, Gonal-F(R), Luveris(R), Ovidrel(R), Rebif(R), Serostim(R) and Saizen(R). In addition to being the world leader in reproductive health, Serono has strong market positions in neurology, metabolism and growth. The Company's research programs are focused on growing these businesses and on establishing new therapeutic areas. Currently, there are eleven molecules in development.

In 2000, Serono achieved worldwide revenues of US$1.240 billion, and a net income of US$301 million, making it the third largest biotech company in the world based on revenues. The Company operates in 45 countries, and its products are sold in over 100 countries. Bearer shares of Serono are traded on the SWX Swiss Exchange (SEO) and its American Depositary Shares are traded on the New York Stock Exchange (SRA).

Please see attached background information concerning:

• EVIDENCE study
• Orphan Drug Status
• Proportion of Relapse-free
• Reduction in Combined Unique Lesion activity
• P value