Rituximab (a monoclonal antibody raised against CD20) is used to treat various immune disorders. In some cases such as treatment of humoral acute rejection of renal transplant, thrombotic thrombocytopenic purpura, vasculitis or cryoglobulinemia, rituximab is often associated with plasma exchange. The pharmacokinetic of the rituximab can be affected by plasma exchange but the knowledge is poor in this matter.