Rituximab (MabThera, Rituxan) is a chimaeric monoclonal antibody increasingly used in the treatment of B-lymphoproliferative disorders and autoimmune diseases. Rituximab is now associated with chemotherapy for the treatment of non-Hodgkin's lymphoma and should be approved soon in maintenance strategies. During its rapid clinical development, rituximab schedules were dictated more often by logistical rather than by scientific considerations. In addition, early clinical phases have shown that rituximab exposure was variable in patients receiving similar doses and that clinical response was related to rituximab concentrations. There is however limited information on rituximab pharmacokinetics and on factors influencing individual exposure to this monoclonal antibody, although a better understanding of these factors is needed to optimise its dosing regimen. This review focuses on the current knowledge on rituximab pharmacokinetics and on factors influencing individual exposure and suggests ways to improve its clinical use.