Determine the efficacy, safety, and tolerability of BG00012 in MS patients.

The study will be divided into two parts: Part 1 will be a 24-week, blinded, placebo-controlled treatment phase followed by Part 2, a 24-week blinded, safety extension phase in which all subjects will receive BG00012.

Inclusion Criteria:

1. Must be 18 to 55 years old, inclusive, at the time of informed consent.
2. Must have a confirmed diagnosis of relapsing-remitting MS according to McDonald criteria #1-4 (McDonald et al, 2001; Appendix 2).
3. Must have a baseline EDSS between 0.0 and 5.0, inclusive.
4. Must have experienced at least one relapse within the 12 months prior to randomization, with a prior cranial MRI demonstrating lesion(s) consistent with MS OR show evidence of Gd-enhancing lesions of the brain on an MRI performed within the 6 weeks.
5. Male and female subjects must be willing to take appropriate measures to prevent pregnancy.

Exclusion Criteria:

1. Primary progressive, secondary progressive, or progressive relapsing MS (as defined by Lublin and Reingold, 1996 [Appendix 3]).
2. History of malignancy.
3. History of severe allergic or anaphylactic reactions or known drug hypersensitivity.
4. History of abnormal laboratory results indicative of any significant cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, gastrointestinal, dermatologic, psychiatric, renal, neurologic (other than MS), and/or other major disease.
5. History of human immunodeficiency virus (HIV).
6. History of drug or alcohol abuse (as defined by the Investigator) within the 2 years prior to randomization.
7. An MS relapse that has occurred within the 50 days prior to randomization AND/OR the subject has not stabilized from a previous relapse prior to randomization.
8. Body weight >100 kg.
9. Positive for hepatitis C antibody and/or positive for hepatitis B surface antigen (HBsAg) at screening.
10. Any of the following abnormal blood tests at screening.
11. Any previous treatment with FUMADERM®, FAG-201, or BG00012.
12. A medication history that precludes entry into the study.
13. Female subjects who are currently pregnant or breast-feeding.