The complete remission (CR) rate after intensive chemotherapy for acute myelogenous leukemia (AML) remains low in elderly patients, mainly because of a higher infectious mortality rate related to neutropenia and an increased incidence of adverse prognostic factors. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to potentially recruit leukemic blasts into cell cycle and improve cytotoxic effects when given during chemotherapy, and to shorten the duration of neutropenia when administered after chemotherapy. Two hundred forty patients aged 55 to 75 years who had newly diagnosed AML were randomly assigned to receive placebo or Escherichia coli-derived GM-CSF (5 micrograms/kg/d by 6-hour intravenous infusion) starting during induction chemotherapy on day 1 and continued through and after chemotherapy until recovery of neutrophils, or evidence of regrowth of leukemia, or up to day 28. Induction chemotherapy consisted of idarubicin (8 mg/m2/d on days 1 to 5) and cytarabine (100 mg/m2/d on days 1 to 7). The study drug was not administered subsequent to the induction course. Patients who achieved a CR received continuous maintenance therapy for 1 year with four quarterly reinduction courses; in the 55- to 64-year age subgroup, patients were randomly assigned to receive or not a consolidation course before maintenance therapy. The CR rate was similar in the GM-CSF and placebo groups (63% and 60.5%, respectively; P = .79). The mortality, rate of resistant disease, and rate of regrowth of leukemia were also similar in both groups. The time to neutrophil recovery was shorter in patients who received GM-CSF (24 v 29 days; P = .0001), but the incidence and characteristics of infectious events were not different. The 2-year disease-free survival (DFS) rate was significantly improved in the GM-CSF group (48% v 21% in the placebo group; P = .003). This effect was highly significant in the cohort of patients aged 55 to 64, but only marginal in patients >/=65 years of age. There was a trend toward a longer overall survival (OS) in the GM-CSF group (P = .082). In summary, the administration of GM-CSF, concomitantly with chemotherapy and thereafter during induction course in AML, shortened the time to neutrophil recovery, but did not improve the CR rate in patients aged 55 to 75. Nonetheless, DFS and OS were significantly prolonged in patients aged 55 to 64 treated with GM-CSF. These results are promising and further evaluation of myeloid growth factors in AML is warranted.