A Study of Rebif® Compared With Avonex® in the Treatment of Relapsing-remitting Multiple Sclerosis (MS)

Inclusion Criteria: * Age between 18 and 55 years * Clinically definite or laboratory-supported definite relapsing-remitting MS according to Poser's criteria * Two or more relapses within the preceding 24 months * Clinical stability or improving neurological state during the 4 weeks before Study Day 1 * Expanded disability status scale (EDSS) score from 0 to 5.5, inclusive * Two or more lesions consistent with MS on a Screening proton density/T2-magnetic resonance imaging (MRI) scan to be performed 28 plus/minus (+/-) 4 days before the Study Day 1 MRI * Willingness and ability to comply with the protocol for the duration of the study * Written informed consent given before any study-related procedure not part of the subject's normal medical care, with the understanding that the subject can withdraw consent at any time without prejudice to future medical care * For female subjects, lack of childbearing potential must be satisfied by either being post-menopausal or surgically sterilized or using a hormonal contraceptive, intra-uterine device, diaphragm with spermicide or condom with spermicide for the duration of the study. Subjects should neither be pregnant nor breast-feeding; confirmation that the subject is not pregnant will be established by a negative serum human chorionic gonadotropin (hCG) pregnancy test within 7 days of Study Day 1 (the pregnancy test will not be required of subjects who will be post-menopausal or surgically sterilized) Exclusion Criteria: * Secondary progressive MS, primary progressive MS or progressive relapsing MS * Prior use of interferon * Treatment with oral or systemic corticosteroids or adrenocorticotropic hormone (ACTH) within 4 weeks of Study Day 1 or within 7 days before the Screening MRI * Psychiatric disorder that is unstable or will preclude safe participation in the study * Significant leucopenia (white blood cell count less than 0.5 times the lower limit of normal) within 7 days of Study Day 1 * Elevated liver function tests (Alanine transaminase \[ALT\], Aspartate transaminase \[AST\], alkaline phosphatase or total bilirubin greater than 2 times the upper limit of normal) within 7 days of Study Day 1 * Prior cytokine or anti-cytokine therapy or glatiramer acetate within the 3 months before Study Day 1 * Immunomodulatory or immunosuppressive therapy within the 12 months before Study Day 1, including but not limited to cyclophosphamide, cyclosporin, methotrexate, azathioprine, linomide and mitoxantrone * Previous use of cladribine or total lymphoid irradiation * Allergy to human serum albumin, mannitol or gadolinium diethylenetriaminepentacetic acid (DTPA) * Intravenous immunoglobulin or any other investigational drug or procedure in the 6 months before Study Day 1 * Systemic disease that can interfere with subject safety, compliance or evaluation of the condition under study, such as insulin-dependent diabetes, Lyme disease, clinically significant cardiac disease or infection with human immunodeficiency virus (HIV) or Human T-cell lymphotrophic virus, Type-1 (HTLV-1)