We administered recombinant human granulocyte colony-stimulating factor (rhG-CSF) at 5 micrograms/kg/day by intravenous drip infusion for 21 consecutive days in autologous bone marrow transplanted patients. The period of posttransplant neutropenia was markedly shortened by the rhG-CSF treatment; mean days required for neutrophil recovery (greater than 500/mm3) of 14.3 days in the rhG-CSF group (n = 21) versus 27.8 days in the historical control group (n = 11). More importantly, the numbers of febrile days between day 15 and day 28 were found to be fewer in the rG-CSF group than in control group. These effects were obtained without delay in the recovery of other blood cell series and without any side effect. We conclude that the posttransplant use of the rhG-CSF is beneficial for prevention and treatment of infectious complications after autologous bone marrow transplantation.