We evaluated the use of granulocyte CSF (G-CSF) after both allogeneic BMT (allo-BMT) and autologous BMT (ABMT) in children. After allo-BMT, G-CSF was used in 15 children who were compared with 20 historical controls. The ABMT patients were two sequential groups: the G-CSF group of 13 children and 11 historical controls. The patients were conditioned with different high-dose chemotherapy regimens with or without total body irradiation. G-CSF was administered at 5 micrograms/kg/day s.c. and was continued until an absolute neutrophil count (ANC) of 1,000 x 10(6)/l was reached. Following allo-BMT, G-CSF accelerated myeloid engraftment with a difference of 5 days at the ANC level of 500 x 10(6)/l (P<0.02) and 9 days at 1,000 x 10(6)/l (P<0.001). In the ABMT patients, G-CSF also accelerated myeloid engraftment. The difference between the G-CSF group and the control group was 6 days at ANC 200 (P<0.05), 11 days at ANC 500 (P<0.02) and 17 days at ANC 1,000 (P<0.005). In the ABMT patients, benefit by G-CSF was also observed in a smaller number of days with fever and days on antibiotics. We conclude that G-CSG significantly accelerated myeloid engraftment, after both allogeneic and autologous BMT in children, and also decreased the duration of febrile illness in the ABMT patients.