Bone marrow colony-stimulating factors (CSF) ameliorate hematologic toxicity of standard chemotherapy regimens and may allow relatively safe use of intensive and more efficacious doses of anticancer drugs. Twenty-four patients with cancers for which no standard regimens were likely to be effective received repeated courses of a combination of cisplatin (150 mg/m2), etoposide (1,500 mg/m2), and cyclophosphamide (5,000 mg/m2) at doses for which bone marrow transplantation is usually used. A total of 10 patients received escalating doses of recombinant human granulocyte CSF (rhG-CSF); 11 patients receiving identical chemotherapy and supportive therapy without rhG-CSF served as controls for the first cycle of therapy. Five of these patients and 3 additional patients also served as their own controls, receiving rhG-CSF for all cycles after the first. No patient received bone marrow transplantation. rhG-CSF shortened the median duration of severe granulocytopenia (less than or equal to 100/mm3) in a dose-related fashion (P less than .03; Kruskal-Wallis test). Patients not receiving rhG-CSF had a median of 8.5 days of granulocytopenia. Those receiving 40 micrograms/kg of rhG-CSF for approximately 20 days from the third day after chemotherapy had a median of 7.0 days (P less than .23) and those receiving 60 micrograms/kg had a median of 5.5 days (P less than .007) of granulocytopenia. An rhG-CSF dose of 20 micrograms/kg had no effect. Recovery to a granulocyte count of at least 500/mm3 took a median of 12 days in the control group and 8 days (P less than .03) in patients receiving rhG-CSF at a dose of 60 mg/kg. The duration of antibiotic therapy (a median, 9.0 days v 5.0 days) was shortened with the two higher and effective doses of rhG-CSF compared with control patients. The duration of hospitalization (median of 20 days v 19 days) was not shortened. These findings that rhG-CSF decreases the risk of granulocytopenia associated with this particular dose-intensive chemotherapy regimen therapy administered without bone marrow transplantation.