Donor-specific bone marrow infusion after organ grafting can induce tolerance in animals. In this randomised controlled study we show it has no benefit in patients undergoing liver transplantation. Of 25 patients, 9 received bone marrow 5 days after a 10 day course of antithymocyte globulin. Immunosuppression was maintained with cyclosporin only. An average of 3.0 rejection episodes per patient was seen in the bone marrow group compared to 3.1 in the controls. Chimerism was not found in peripheral blood or bone marrow of recipients using erythrocyte antigen markers, PCR for donor class II DNA or Y-probe in-situ hybridisation in one female recipient of male liver and bone marrow.