Recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) significantly shortens the number of days required to achieve an absolute neutrophil count of >500/mm(3) after autologous bone marrow transplantation (ABMT); however, the ability of rhGM-CSF to enhance neutrophil and macrophage function in vivo has been incompletely characterized. In this retrospective study, the authors compared the incidence of infection from the day of transplantation to 28 days posttransplantation between two groups of previously studied patients who underwent ABMT at the Fred Hutchinson Cancer Research Center. A control group that received no cytokine was compared with a study group that received rhGM-CSF while participating in phase I, II, or III trials. During the posttransplantation period when both study groups had severe neutropenia, 40% (38 of 95) of control patients were found to have an infection, whereas only 13% (6 of 46) of rhGM-CSF patients developed an infection (p = 0.001). Most infections occurred before an absolute neutrophil count of >100/mm(3) was achieved. There was a trend toward fewer fungal infections (14% vs. 4%; p = 0.093); gram-negative bacterial infections (6% vs. 0%; p = 0.083); pulmonary infections (12% vs. 2%; p = 0.062); fewer days of amphotericin B (p = 0.0305); and fewer days of intravenous antibiotics (p = 0.0791) in rhGM-CSF-treated patients. These results support in vivo findings that the function-enhancing effect of rhGM-CSF may reduce infection-related complications.