Randomized Study Designed to Look at Disease Progression Using 2 Currently FDA Approved Drugs for the Treatment of RRMS

Inclusion Criteria: Patients must have a diagnosis of clinically definite MS with a relapsing disease course as determined by the Poser criteria Patients must be on high dose interferon therapy (Betaseron® 250 µg or Rebif® 44 µg) for at least 1 year prior to study entry Patients must have experienced at least one documented relapse during the past year prior to screening. Pseudo-relapses must be ruled out. A gadolinium enhancing lesion is not required. Patients must be ambulatory, with a Kurtzke EDSS score between 0-5 inclusive Patients must be between the ages of 18 and 50 years inclusive Women of childbearing potential must practice an acceptable method of birth control. Acceptable methods include oral contraceptive, contraceptive patch, long-acting injectable contraceptive, double-barrier method (condom or IUD with spermicide), or partner's vasectomy Patients must be relapse-free and off corticosteroids (IV or oral) for at least 30 days prior to the screening visit Patients must be relapse-free and off corticosteroids between the screening and baseline visits Patients must be willing and able to give written informed consent Exclusion Criteria: Use of experimental or investigational drugs, and/or participation in an investigational drug study within 6 months prior to study entry Previous treatment with glatiramer acetate (injectable) Previous treatment with immunomodulators (except IFNβ), immunosuppressive agents, IVIG, or plasma exchange in the 6 months prior to screening; previous treatment with cladribine in the past 2 years Previous total body irradiation or total lymphoid irradiation Chronic corticosteroid (IV, IM, and/or PO) treatment (more than 30 consecutive days) in the 6 months prior to study entry Pregnancy or breastfeeding Life-threatening or other clinically significant disease Any condition which the investigator feels may interfere with participation in the study, including alcohol and/or drug abuse A known sensitivity to gadolinium (gadolinium acid) A known history of sensitivity to mannitol Inability to successfully undergo MRI scanning