Transfusional therapy regimens have been investigated in a series of 385 patients treated for acute leukemia (AL). During remission induction, fatal hemorrhages occurred in 0.7% of the patients whereas, during the same time, deaths due to infections were four times more frequent. Platelet concentrates (PC) were usually given on the basis of clinical indications. When the risk of hemorrhage was especially high, as during the induction phase of acute promyelocytic leukemia, prophylactic platelet transfusions seemed to be necessary. Alloimmunization developed in 17% to 52% of the patients depending on their cytologic type and in these cases, PC prepared from single donors had to be used. Among the 57 patients with aplastic anemia (AA), bone marrow transplantation was indicated in 17, and 5 of the 10 grafted patients died from hemorrhages. In AA, as the risk of sensitization to platelet alloantigens was higher, PC prepared from single donors were systematically preferred to standard PC. If bone marrow transplantation was planned, PC from histocompatible donors were ordered.