Bone marrow transplantation is impossible without effective support with blood components during the period of pancytopenia before graft function appears. We analyzed 39 patients with leukemia and three patients with severe aplastic anemia with regard to the pre- and postgrafting requirements for RBC and PLT transfusions. Overall a median of eight RBC and four PLT concentrates were necessary in all 42 patients after allogeneic BMT (ranges, 1-32 RBC and 1-11 PLT units). Requirements were identical irrespective of the underlying disease (ALL, AML, CML, SAA). Transfusion need for RBC and PLT concentrates increased in patients over 30 years old and with a major red blood group AB0 barrier between marrow donor and recipient. The presence of grade II-IV GvHD increased RBC requirements significantly, but not PLT requirements. In addition these patients were dependent on RBC transfusions for significantly longer periods. Only one patient required therapeutic granulocyte transfusions. In a CMV-negative patient with a CMV-negative marrow donor, who died of veno-occlusive disease, cytomegalovirus was transmitted inadvertently by a seropositive PLT concentrate in his final course. Our transfusion strategy included frozen deglycerolized RBC concentrates and single donor PLT concentrates, collected mainly from the marrow donor by a cell separator. All blood products were irradiated in vitro with 1500 cGy before transfusion. An optimal transfusion policy starting before BMT can contribute to successful bone marrow transplantation.