Superiority of single-donor apheresis platelets (SDAP) over pooled platelet concentrates (PPC) transfusions is largely assumed, but unproven. We hypothesized that prophylactic SDAP and PPC transfusions are clinically equivalent after allogeneic hematopoietic stem cell transplants (HSCT). We studied all transfusions administered to 33 patients with AML/MDS during the first 100 days after busulfan-based, myeloablative HSCT. All donor recipient pairs were ABO identical. Transfusion threshold was a platelet count <= 15 x 10(9)/l. The corrected increment (CCI) was used for all comparisons. Median time to platelet engraftment was 13 days (n = 30). PPC transfusions (n 105) were ABO compatible, while 10% of 41 SDAP were not (P = 0.006). Median post-transfusion platelet count was 51K/mu l (5-118K) after SDAP and 36K/mu l (3-115K) after PPC (P = 0.0004). Median CCI was 14.178 (SDAP) versus 7.793 (PPC) (P = 0.0001). Median time to another transfusion was 3 days (SDAP) and 2 days (PPC; P = 0.3). In the week following any given transfusion, the median number of new transfusions was similar (n = 2), as well as the need of further transfusion (16 versus 24%, P = 0.2). A total of 17% of SDAP and 30% of PPC transfusions were labeled 'ineffective' (P = 0.1). There were two non-lethal hemorrhage episodes (6%). SDAP transfusions produced better platelet counts, but SDAP and PPC were equally effective in preventing hemorrhage.