Infections during granulocytopenia are major complications of autologous bone marrow transplantation (ABMT). Since recombinant human granulocyte-macrophage colony-stimulating factor (rhuGM-CSF) has proved to accelerate bone marrow recovery after cytostatic chemotherapy, we studied its effects on hematopoietic regeneration and on infectious complications after total body irradiation (TBI) and high-dose chemotherapy followed by ABMT. Eighty-one patients with acute lymphoblastic leukemia (ALL) in complete remission (CR) or with non-Hodgkin's lymphoma (NHL) in CR or partial remission were randomized in a double-blind, placebo-controlled trial. They received either rhuGM-CSF 250 micrograms/m2 (Escherichia coli-derived) daily by continuous infusion after ABMT, or placebo. Treatment was continued until the neutrophil counts reached greater than 500/microL for 1 week. The maximum treatment duration was 30 days. Thirty-nine patients in the rhuGM-CSF group and 40 patients in the placebo group were evaluable. The median time needed to reach a neutrophil count of 500/microL was 15 days with rhuGM-CSF and 28 days with placebo (P = .0001). Bacterial infections occurred in 14 (35.9%) of the patients with rhuGM-CSF and in 25 (62.5%) of the patients given the placebo (P = .024). Nine of the 14 bacterial infections in the rhuGM-CSF group and 20 of the 25 infections in the placebo group were diagnosed within the first 10 days after ABMT. Capillary leakage and a reversible fluid retention were seen in five of the rhuGM-CSF-treated patients. Patients treated with rhuGM-CSF had lower serum protein and albumin levels than patients in the placebo group. There was no statistically relevant difference in overall survival between the two groups (P = .47). Relapse occurred in 14 (34%) patients with rhuGM-CSF and in 18 (45%) patients with placebo. We conclude that continuous infusion of rhuGM-CSF after ABMT accelerates the regeneration of granulocytes and reduces the number of bacterial infections.