The primary objective of this study is to determine whether combination treatment (adding methylprednisolone to Avonex) reduces progression of disability over 4 years compared to Avonex alone. The study will also investigate whether combination therapy has any impact on the incidence of relapse and brain atrophy as measured by MRI.

Approximately 340 therapy-naïve MS patients with relapsing-remitting form of the disease will be randomized to receive Avonex alone or Avonex plus methylprednisolone (MP). Patients will receive MP as 500 mg po for 3 days every month or matching placebo. The patients are followed on a 3-monthly basis for 4 years with disability as the primary parameter of efficacy over that time.

• Experimental: interferon-beta-1a in combination with methylprednisolone
• Placebo Comparator: interferon-beta-1a in combination with placebo

Inclusion Criteria:

• Informed consent
• Relapsing remitting MS according to Poser criteria or McDonell criteria and naïve to therapy
• Disability EDSS score of 4.0 or less at baseline
• Clinical activity as defined by at least one relapse in the last year

Exclusion Criteria:

• Relapse in the month prior to enrolment
• Treatment with immunosuppressive drugs for MS
• History of major depression
• Former severe reactions to corticosteroids
• Pregnant women
• Diabetes mellitus, and drug or alcohol dependency
• Known or suspected allergy to trial products