Two series of five consecutive patients with small cell lung cancer were treated with an "accelerated" chemotherapy regimen of cyclophosphamide-doxorubicin-vincristine (CAV) and cisplatin-etoposide (PE) alternated possibly every week. In the first group of patients (median age 49 years, range 46-52) recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) was given as soon as grade IV leukopenia occurred, while in the second group (median age 59 years, 55-68) no growth factor was administered. The mean interval between chemotherapy courses and the mean duration of chemotherapy were 10 and 57 days, respectively, in the patients supported with GM-CSF compared with 13 and 72 days in the control group. One GM-CSF treated patient was withdrawn after the third cycle because of severe toxicity. The mean white blood cell and platelet nadirs were 600 and 46,000/microliters in the first group vs. 840 and 105,000/microliters in the controls. Overall chemotherapy dose-intensity was increased by two fold in the patients given GM-CSF compared with a 1.5 fold increase in the control patients. In all cases, irrespective of their treatment, there was an impaired colony forming capacity of circulating and marrow haemopoietic progenitor cells when grade IV leukopenia occurred, with recovery after the end of leukopenia. This pilot study suggests that accelerated CAV/PE chemotherapy is feasible both with and without GM-CSF. Different GM-CSF schedules as well as combinations of different haemopoietic growth factors may further improve dose-intensity.