The CD20 cell marker appears early in the process of B cell development. In this review we focus on the results of attempts to utilize B cell depletion based on the use of a chimeric monoclonal antibody (MAb) specific for human CD20, rituximab, for the treatment of patients with autoimmune diseases. In 1997, rituximab was approved for the treatment of low-grade B cell non-Hodgkin's lymphoma. Following these encouraging results, rituximab started to be used experimentally in other diseases presumed to be due to B cell pathology. The first autoimmune disease to be treated effectively was chronic idiopathic thrombocytopaenia. More recent success has been demonstrated in patients with rheumatoid arthritis and systemic lupus erythematosus.