Patients with acute myelogenous leukemia undergoing induction chemotherapy have significant decreases in alloimmune platelet refractoriness if they receive filter-leukoreduced or UV-B-irradiated vs standard platelet transfusions (3%-5% vs 13%, respectively; P ≤ .03) with no differences among the treated platelet arms (Trial to Reduce Alloimmunization to Platelets). Therefore, measuring antibody persistence might identify the best platelets for transfusion. Lymphocytotoxic (LCT) antibody duration was evaluated for association with patient age, sex, prior transfusion and pregnancy history, study-assigned platelet transfusions, and percentage LCT panel reactive antibodies. During the Trial to Reduce Alloimmunization to Platelets, 145 patients became antibody positive; and 81 (56%) of them subsequently became antibody negative. Using Kaplan-Meier estimates, projected antibody loss was 73% at 1 year. Major factors associated with antibody persistence were prior pregnancy and percentage panel reactive antibody positivity, whereas neither the assigned type of platelets transfused during the 8 weeks of the trial nor prior transfusion history was predictive. After 5 to 8 weeks, the number and type of blood products transfused had no effect on either antibody development or loss. A majority of patients with acute myelogenous leukemia who develop LCT antibodies during induction chemotherapy will lose their antibodies within 4 months regardless of the type or number of blood products they receive.