For more than a decade the only therapies that were available for multiple sclerosis (MS) were two immunomodulatory drugs-interferon beta and glatiramer acetate-and the immunosuppressant mitoxantrone. Natalizumab, a monoclonal antibody against alpha4 integrin, has been approved by the US Food and Drug Administration and the European Medicines Agency on the basis of its higher efficacy than the available treatments and its good safety profile. Monoclonal antibodies that are already licensed to treat other diseases, such as cancer and autoimmune diseases, are being tested for the treatment of MS. Additionally, novel targets are currently being investigated for MS. The therapeutic use of monoclonal antibodies was initially viewed with great scepticism owing to the high rates of sensitisation against mouse proteins, their pharmacokinetic properties, and the difficulties in their production. However, most of these problems have been overcome, and monoclonal antibodies are now among the most promising therapies for MS.