Rituximab, chimeric anti-human CD20, is approved for treatment of B-cell lymphoma in adults. It is being used experimentally in other various immune-related diseases such as immune thrombocytopenic purpura, systemic lupus erythematosus, myasthenia gravis and rheumatoid arthritis. In transplant recipients, it is used for treatment of post-transplant lymphoproliferative disease, to anecdotally reduce pre-formed anti-HLA and anti-ABO antibodies and for the prevention and treatment of acute rejection. This article primarily reviews the science behind rituximab: its history, pharmacokinetics and potential mechanism of action. A need for controlled clinical trials is clearly indicated before the widespread use of this drug in transplant.