Neutropenia is one of the risk factors for severe therapy-related morbidity in childhood malignancies. We have studied the potential of GM-CSF to shorten the neutropenic period after normal-dose chemotherapy in children who were treated for solid tumors. Patients with osteosarcomas, with Ewing sarcomas, or with rhabdomyosarcomas received 10 daily subcutaneous doses GM-CSF (Leucomax, 5 micrograms/kg) after a course of normal-dose chemotherapy in an open-label study. Because these patients were treated with different combinations of chemotherapeutic agents, they were randomized before each pair of identical courses of chemotherapy to receive GM-CSF after the first or after the second course. Fourteen such combinations could be evaluated in eight patients. The results show that GM-CSF significantly reduced the mean duration of the chemotherapy-induced neutropenia (mean reduction +/- SEM in days: 2.2 +/- 0.6, P = .003). There was no significant difference between the mean number of days with fever in either group. GM-CSF was well tolerated by all patients. We conclude that GM-CSF reduced the mean neutropenic period in children with solid tumors who were treated with standard-dose chemotherapy.