To determine the efficacy and optimal daily dose of recombinant human granulocyte colony-stimulating factor (rG-CSF) after intensive chemotherapy, a prospective randomized study was conducted with daily intravenous administration of 2, 5 or 10 micrograms/kg G-CSF after induction therapy, and 0, 2, 5 or 10 micrograms/kg after consolidation therapy, until neutrophil counts recovered to more than 2000/mm3. The subjects were 41 adult patients with newly diagnosed acute lymphoblastic leukemia (ALL). After the induction therapy, neutrophil recovery to more than 1000/mm3 was significantly faster in the 5 (P = 0.047) and 10 micrograms/kg groups (P = 0.011) than in the 2 micrograms/kg group, but did not differ between the 2 former groups. The median days of neutrophil recovery to more than 1000/mm3 were 8.5, 9 and 12 days, respectively. After the consolidation therapy, neutrophil recovery to more than 1000/mm3 was significantly faster in the 2, 5 and 10 micrograms/kg groups than in the no rG-CSF group (P < 0.001, respectively), but did not differ among the 3 former groups. The median days of neutrophil recovery to more than 1000/mm3 were 12, 11, 10, and 23 days, respectively. Febrile neutropenia and incidence of documented infection tended to be less in the 5 and 10 micrograms/kg groups than in 0 and 2 micrograms/kg groups. A dose of 5 micrograms/kg rG-CSF given by a 30 min infusion daily seems to be an effective and optimal daily dose to accelerate neutrophil recovery after intensive remission induction and consolidation chemotherapy in adults with acute lymphoblastic leukemia (ALL).