Objective. Compare the speed of neutrophil recovery and the unwanted secondary effects in two groups of acute leukemia patients treated with intensive chemotherapy and G-or GM-CSF. Patients and methods. Patients were randomly assigned to receive subcutaneous G-CSF at a daily dose of 300 mu g for adults and 150 mu g for children or GM-CSF at 400 and 200 mu g respectively, starting With chemotherapy and stopping when the absolute neutrophil count (ANC) reached 500/mu L. Secondary effects were attributed to growth factors Only when not coincidental with infection, chemotherapy or hemoderivative transfusion. Results. 34 patients were included in the G-CSF arm End 37 in the GM-CSF arm. Distribution by sex, age, type of acute leukemia, induction or post-induction therapy, as well as initial neutrophil count were comparable among the two groups. Mean time for ANC > 500/mu L was 19 days for G-CSF group and 16 days for GM-CSF group (p = 0.08). There were no statistically significant differences in secondary unwanted side effects between the two groups. There were two cases of growth factor related-fever in the G-CSF group and five in the CM-CSF group (p = 0.25). There was a case of systemic reaction in the C-CSF group. Twenty-nine patients in each group presented febrile neutropenia episodes (p = 0.45). The only factor that showed significance on neutrophil recovery speed was type of leukemia (p = 0.04). Conclusions. We found no clear advantage of one growth factor over the other for this indication.