The purpose of this study is to find out if weekly Avonex works as well as three times a week Rebif in subjects with relapsing multiple sclerosis.

This is a Phase 4, multicenter, prospective and retrospective, long-term observational study of Avonex® and Rebif® to determine the efficacy, tolerability, and safety in subjects with relapsing MS.

Inclusion Criteria:

• Must have been receiving AVONEX® or Rebif®.
• Must have a confirmed diagnosis of relapsing-remitting MS using the Poser criteria.
• Must have experienced at least 2 relapses within the 3 year period prior to the initiation of treatment.
• Must have an EDSS score of 0.0 to 5.5, inclusive.

Exclusion Criteria:

• History of severe allergic or anaphylactic reaction or hypersensitivity to human albumin, to any interferon, or to other components of the drug formulation.
• History of poorly controlled hypertension and/or other clinically significant major disease.
• History of uncontrolled seizures within the 3 months prior to enrollment.
• History of suicidal ideation or an episode of severe depression within the 3 months prior to enrollment.
• Serious local infection or systemic infection within 8 weeks prior to enrollment.
• Treatment with certain other agents to treat MS symptoms or underlying disease.
• Treatment with any investigational product
• Previous participation in this study.
• Other Protocol-defined inclusion/exclusion criteria may apply.

subjects with relapsing remitting Multiple Sclerosis taking AVONEX® or Rebif®.