In a patient aged 22 years with acute myeloblastic leukaemia during complete remission an allogenic transplant of bone marrow identical in the HLA antigen range was rejected despite administration before transplantation of a full marrow-ablating dose of busulphan (16 mg/kg) and severe graft-versus-host disease. Graft rejection manifested itself as disappearance of its haemopoietic function which was confirmed during the life and on autopsy. The case deserves attention in view of the rarity of HLA-identical marrow graft rejections in patients treated for leukaemias.