We performed a prospective, randomized, open, blinded end point (PROBE) study to assess the efficiency of transfusing high doses of platelets in patients with thrombocytopenia, either acute leukemia (AL) or those undergoing autologous hematopoietic stem cell transplantation (AT). Patients were randomly assigned to receive transfusions with a target dose of 0.5 x 10(11)/10 kg (arm A) or 1 x 10(11)/10 kg (arm B). A total of 101 patients were included, of whom 96 were given at least one transfusion. The median time between the first transfusion and when the platelet count reached at least 20 x 10(9)/L increased from 63 hours to 95 hours in the arm B group (P = .001), and the median number of transfusions was lower in this group (2; P = .037). The total number of transfused platelets did not differ between groups (14.9 x 10(11) for arm A versus 18.5 x 10(11) for arm B; P = .156). In such patients, a prophylactic strategy of high doses of platelets could improve platelet transfusion efficiency.