Multiple sclerosis is an inflammatory and demyelinating disease of the central nervous system. Impaired cell-mediated and humoral immunity play an important role in the pathogenesis of the disease. B lymphocytes play an important role in the presentation of own antigens to T lymphocytes and in the production of pro-inflammatory cytokines and autoantibodies. In primary progressive multiple sclerosis a degenerative reaction with axonopathy and neuronal damage are predominant features. A monoclonal antibody against CD20 B lymphocytes was used in clinical studies on relapsing multiple sclerosis (OPERA I and II studies) and on primary progressive MS (ORATORIO study). A statistically significant reduction of the annualised relapse rate, clinically defined progression and contrast-enhanced T2-weighted magnetic resonance imaging lesions was demonstrated for relapsing multiple sclerosis in the group of patients treated with ocrelizumab compared to patients receiving interferon beta-1a. A statistically significant reduction of clinically defined progression, T2-weighted lesions and changes in brain volume in magnetic resonance imaging was found for primary progressive multiple sclerosis in the group of patients treated with ocrelizumab compared to placebo. The safety profile of ocrelizumab was satisfactory and was not significantly different from the profile in the control groups. It seems that ocrelizumab affects CD20 B lymphocytes in a clinically beneficial way and that phase 3 clinical study results may be the basis for its registration and common use in clinical practice.