Patients with metastatic germ cell tumors undergoing five-day chemotherapy with etoposide, vinblastin, bleomycin and cisplatinum were given recombinant GM-CSF (mammalian glycosylated, Sandoz/Schering-Plough) at increasing dose levels of 75, 150, 300 or 600 micrograms protein/day in a double blind placebo controlled study. The drug was administered SC twice a day for 5 days starting 24 hours after completion of chemotherapy. Fourteen treatment courses, 10 with GM-CSF and 4 with placebo in 11 patients were evaluable for assessment of toxicity and hematological recovery, and 2 were not evaluable due to complications of progressive germ cell tumor. One patient receiving the highest dose level developed a delayed skin reaction at the site of injection. Fever under 38.5 degrees C and a flu-like syndrome were observed in 4/5 patients receiving the higher two dose levels, but not with lower dose levels or placebo. Two patients experienced mild bone pain. The neutrophil nadir was similar in the two groups, but the duration of neutropenia was significantly shorter in the GM-CSF group. At day 21 of chemotherapy the neutrophil count was 2.57 +/- 1.37 10(9)/l with GM-CSF, and 1.01 +/- 0.56 10(9)/l with placebo (p less than 0.05). Patients receiving GM-CSF could be retreated on day 21, whereas in patients given placebo, retreatment was delayed for an average of 7 days (p less than 0.05). Thus, a 5-day treatment with GM-CSF given subcutaneously resulted in a significant shortening of neutropenia and allowed for the timely administration of the subsequent cycle of chemotherapy.