Nineteen noninfected adults receiving initial induction chemotherapy for acute nonlymphocytic leukemia (ANLL) were randomized to receive either prophylactic granulocyte transfusion or platelet transfusion alone on an alternate-day schedule. An average of 11 granulocyte transfusions (range 3--19) were administered/patient with a mean dose of 11.5 X 10(9) granulocytes/transfusion. The groups were identical with respect to age, sex, number of days on study, granulocytopenic days, percent of days receiving systemic antibiotics, febrile days, complete remission rate, and incidence of minor infection. Significant transfusion reactions were much increased in the granulocyte transfusion group (7/10 versus 1/9 in controls) and were associated with the development of lymphocytotoxic antibodies (7/10 versus 4/9 controls), refractoriness to platelet transfusion, repeated fevers, and a pulmonary infiltrate in one patient. Alloimmunization to granulocytes occurred as early as the second week in some patients complicating platelet support during induction and maintenance. No severe infections occurred in the granulocyte transfusion group while three fungal infections occurred in the controls. The high rate of alloimmunization suggests that histocompatibility considerations indicate that prophylactic granulocyte transfusion should not be routine therapy and should be studied only in investigational settings.