The effect of granulocyte transfusions on the course of infection in patients under treatment for acute leukemia was evaluated by comparing 19 febrile episodes in 15 patients receiving antibiotics alone with 18 febrile episodes in 13 patients receiving antibiotics in combination with granulocyte transfusions from ABO-matched donors. Both groups had a similar age, sex distribution and duration of disease prior to the febrile episode. About two-thirds of the patients in both groups had acute myeloblastic leukemia. 94% of the patients in the transfused group and 74% of the control group survived the febrile episode. In patients with positive blood cultures all transfused patients survived as compared to only 57% in the control group (p=0.05). In patients with persistent bone marrow failure 92% of the transfused patients survived as compared to 73% in the control group. Granulocyte transfusions had no effect on the outcome of febrile episodes in patients with negative blood cultures or early recovery of marrow function. These data appear to support the contention that granulocyte transfusions are beneficial in patients with blood culture-proved sepsis with persistent neutropenia.