Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. Until recently, most therapeutic interventions have targeted T cells in the treatment of MS. Recent data show that B cells also have a role in the pathogenesis of MS. The cerebrospinal fluid and CNS of MS patients contain B cells, plasma cells and immunoglobulins, and recent data indicate that B cells are involved in antigen presentation and T-cell activation, cytokine production, antibody secretion, demyelination and remyelination in MS. These advances in the understanding of B cells and their role in the pathophysiology of MS provide a strong rationale for B cell-targeted therapies. Recent clinical trials with rituximab highlight the possibility that B cells should be an important therapeutic target in patients with MS.