SUMMARY.The relationship between the 1 and 20 h post‐transfusion platelet count and three parameters used to define refractory transfusions, namely the corrected increment (CI), platelet increment (PI), and percentage platelet recovery (%REC), was studied in 437 non‐HLA matched platelet transfusions given to 102 patients with bone marrow failure. The percentage agreement between common definitions of refractoriness was calculated based on these parameters. As the maintenance of platelet counts above 20 times 109/1 is a relevant clinical goal for platelet support, the values of the CI, PI and %REC, which best corresponded to 1‐ and 20‐h post‐transfusion counts of 20 times 109/1, were identified. A 1‐h post‐transfusion CI<3 (PI<7 times 109/1 or % REC<8%) corresponded to clinically unsuccessful transfusions with a 1‐h platelet count<20 times 109/1. A 1‐h CI≥5.5 (PI≥12 times 109/1 or %REC≥14%) corresponded to clinically successful transfusions with a 20‐h post‐transfusion count of ≥20 times 10/1. These data tie together the end points reported in the literature for def