Ofatumumab is an anti-CD20 IgG1kappa human monoclonal antibody that is being considered by the US Food and Drug Administration and the European Medicines Agency for marketing approval as a treatment for chronic lymphocytic leukemia. The mAb is also being studied as a treatment for lymphoma, rheumatoid arthritis and multiple sclerosis. The candidate targets the same antigen as rituximab, but ofatumumab binds a novel, membrane-proximal epitope, and dissociates from its target at a slower rate compared to rituximab. Ofatumumab might be approved in the US by August 2009.