Rituximab is a cytotoxic chimeric human mouse monoclonal antibody with a high affinity for CD20, a pan-B-cell surface antigen. It was developed originally for the treatment of B-cell lymphomas. The killing of B cells by rituximab is thought to depend on both of the specific recognition of B cells by this monoclonal antibody and natural killer (NK) cell-mediated antibody -dependent cellular cytotoxicity (ADCC) of those cells. There is considerable evidence that the interaction of B-cell-bound monoclonal antibodies with NK cell CD16 (FcγRIIIA) is a critical event leading to ADCC following treatment with rituximab. Rituximab appears to have activity in a variety of autoimmune diseases associated with autoantibody production including RA, SLE, polymyositis/dermatomyositis, sjogren’s syndrome, and cryoglobulinemic vasculitis.