This is a Phase II, randomized, double-blind, parallel group, placebo controlled, multicenter study to evaluate the safety and efficacy of Rituximab in adults with RRMS.

Inclusion Criteria:

• Ability and willingness to provide written informed consent and to comply with the schedule of protocol assessments
• Age 18--55 years, inclusive
• Diagnosis of relapsing MS, as defined by McDonald Criteria 1--4
• History of at least one relapse in the subject's medical records during the 1 year prior to randomization
• EDSS at screening between 0 and 5.0 points, inclusive
• For subjects of reproductive potential (males and females), ability and willingness to use a reliable means of contraception (e.g., hormonal contraceptive, patch, vaginal ring, intrauterine device, physical barrier) during the study, including the safety follow-up period, and for up to 1 year after their last dose of study drug, even if they have discontinued early from the study

Exclusion Criteria:

• Pregnancy or lactation
• Incompatibility with MRI
• Lack of peripheral venous access
• History of severe, allergic, or anaphylactic reactions to humanized or murine monoclonal antibodies
• Known active bacterial, viral, fungal, or mycobacterial infection, or other infection (including atypical mycobacterial disease, but excluding fungal infections of nail beds or recurrent herpes infections), or any major episode of infection requiring hospitalization or treatment with IV antibiotics within 30 days prior to screening or oral antibiotics within 14 days prior to screening
• History or presence of recurrent or chronic infection (e.g., hepatitis B or C, HIV, or syphilis)
• History of cancer, including solid tumors and hematologic malignancies (except fully resolved and resected cutaneous basal cell and squamous cell carcinomas of the skin)
• History of alcohol or drug abuse within 6 months prior to screening
• History of or currently active primary or secondary immunodeficiency
• Presence of significant, uncontrolled disease of the cardiovascular, pulmonary, renal, hepatic, endocrine, or gastrointestinal systems
• Diagnosis of secondary progressive, primary progressive, or progressive relapsing MS
• History or presence of vascular disease potentially affecting brain or spinal cord (e.g., stroke, transient ischemic attack, severe carotid stenosis, aortic aneurysm, intracranial aneurysm, hemorrhage, arteriovenous malformation)
• History or presence of myelopathy due to spinal cord compression by disk or vertebral disease
• History of severe, clinically significant CNS trauma (e.g., cerebral contusion, spinal cord compression)
• History of intracranial or intraspinal tumor (e.g., meningioma, glioma)
• History or presence of potential metabolic cause of encephalopathy or myelopathy (e.g., untreated vitamin B12 deficiency, untreated thyroid deficiency)
• History or presence of infectious causes of encephalopathy or myelopathy (e.g., syphilis, Lyme disease, human T-cell lymphotropic virus type 1 [HTLV-1], herpes zoster myelopathy)
• Neuromyelitis optica
• History or presence of systemic autoimmune disorders potentially causing progressive neurologic disease (e.g., lupus, antiphospholipid antibody syndrome, Sjogren�s syndrome, Behcet disease)
• History or presence of sarcoidosis
• Relapse within 30 days prior to randomization
• Previous treatment with rituximab (MabThera(R)/Rituxan(R))
• Treatment with any investigational agent within 90 days of randomization or five half-lives of the investigational drug (whichever is longer)
• Receipt of a live vaccine within 30 days prior to randomization
• Previous treatment with lymphocyte-depleting therapies (e.g., Campath(R), anti-CD4, cladribine, total body irradiation, bone marrow transplantation)
• Treatment with cyclophosphamide or mitoxantrone within 12 months of randomization
• Systemic corticosteroid therapy within 30 days of randomization
• Treatment with IFN-Beta; or Copaxone(R) within 60 days of randomization
• Treatment with IVIG within 60 days of randomization
• Plasmapheresis within 60 days of randomization
• Treatment with non-lymphocyte depleting immunosuppressive therapies (e.g., azathioprine, mycophenolate mofetil, cyclosporine) within 90 days prior to randomization
• Statins or hormone replacement therapy started within 30 days of randomization
• Positive pregnancy test
• B-cell count <1.1% (reported as percent CD19)
• Vitamin B12 below the lower limit of normal with an abnormal methylmalonic acid level
• Positive rapid plasma reagin
• Serum creatinine >1.4 mg/dL for women or >1.6 mg/dL for men
• Aspartate aminotransferase (AST/SGOT) or alanine aminotransferase (ALT/SGPT) >2.5 x the upper limit of normal
• Platelet count <100,000/mL
• Hemoglobin <8.5 g/dL
• Neutrophils <1.5 x 10^3/mL
• Serum IgG levels below 5.65 mg/mL and serum IgM levels below 0.55 mg/mL
• Findings on brain MRI scan consistent with clinically significant conditions other than MS
• Electrocardiogram (ECG) showing significant abnormality that the treating investigator determines may jeopardize the subject's health (i.e., acute ischemia, left bundle branch, or bifascicular block)