The two major methods of modifying donor blood products to prevent alloimmunization are leukocyte reduction or ultraviolet B (UVB) irradiation. Two studies have suggested that leukocyte reduction to levels <5 x 10(6) may be required to prevent alloantibody production. Three prospective, randomized transfusion trials demonstrated a statistically significant (P < 0.05) decrease in both platelet refractoriness and lymphocytotoxic antibody production in patients who received leukocyte-reduced blood components as compared to those who received standard unmodified blood products. The results of the Trial to Reduce Alloimmunization to Platelets (TRAP trial) further confirm the potential beneficial effects of leukocyte-reduced and UVB-irradiated blood products in preventing alloimmune platelet refractoriness. Five hundred thirty antibody-negative patients undergoing induction chemotherapy for acute myeloid leukemia were randomly assigned to receive either unmodified platelet concentrates, filtered leukocyte-reduced platelet concentrates, UVB-irradiated platelet concentrates, or filtered leukocyte-reduced platelets obtained by apheresis. Patients who received modified platelet components had statistically significantly lower rates of both alloimmune platelet refractoriness and lymphocytotoxic antibodies than did patients who received unmodified platelet components. There were no differences in any study endpoints among patients who received any of the three modified platelet components. The investigators concluded that leukocyte-reduced and UVB-irradiated platelet components were equally effective in preventing alloimmune-mediated platelet refractoriness; platelets obtained by apheresis provided no additional benefit.