In a placebo-controlled double-blind dose-finding trial, 15 patients with ovarian cancer stage III or IV received daily s.c. 1.5, 3, or 6 micrograms/kg recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF). At each dose step three patients received recombinant human GM-CSF, and two received placebo. Chemotherapy comprised 6 cycles of carboplatin, 300 mg/m2, and cyclophosphamide, 750 mg/m2, by i.v. bolus on day 1 every 4 weeks. GM-CSF, given on days 6-12 on an outpatient basis, raised the mean leukocyte count on days 7, 10, and 15 and the mean neutrophil count on days 7 and 10 at all dose levels as compared with the control group. Neutrophil counts of less than 0.5 x 10(9)/liter occurred in 20 of 22 cycles in the control group and in 5 of 17 cycles at the 6-micrograms/kg/day GM-CSF dose level (P less than 0.0005). In comparison with the control group, the mean eosinophil count was higher on days 10 and 15 at all GM-CSF doses, as was the mean monocyte count on day 15. The mean platelet count was raised at the 3- and 6-micrograms GM-CSF doses on days 15 and 22. Chemotherapy dose reduction or postponement due to myelotoxicity occurred in 9 of 28 cycles in the placebo groups versus 5 of 44 cycles in the GM-CSF group (not significant). Local skin infiltrates at the GM-CSF injection sites occurred in 8/9 patients, leading to premature removal of two patients from the study. Capillary leakage of 131I-albumin was increased in all patients 5 days after the first chemotherapy course but was not significantly affected by 4 days of GM-CSF treatment. Tumor necrosis factor alpha and C-reactive protein serum levels increased during GM-CSF administration at the 6-micrograms dose level, but interleukin 6 serum levels were not affected. We conclude that a dose of 3 and 6 micrograms/kg/day GM-CSF reduces the severity of neutropenia and thrombocytopenia after carboplatin-cyclophosphamide. This GM-CSF dose does not induce additional capillary leakage.