30 patients with chemotherapy-related leukopenia (white cells 1.0 x 10(9)/l or lower) and fever (temperature 38.5 degrees C or higher) were treated in a double-blind randomised trial with standard antibiotics and 7 days of intravenously administered recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF, 2.8 micrograms/kg per day) or placebo. GM-CSF administration resulted in a faster percentage increase of peripheral neutrophil count after 2 and 3 days of treatment, except in patients treated with ablative chemotherapy and autologous bone-marrow transplantation. However, GM-CSF did not shorten the period of fever or antibiotic administration. No side-effects were observed; in particular tumour necrosis factor alpha and interleukin-6 did not increase in the 5 GM-CSF patients tested. These data suggest that a subgroup of patients with chemotherapy-related leukopenia and fever may benefit from GM-CSF treatment in view of the observed effects on neutrophil count.