The aim of this study was to determine the usefulness of recombinant human granulocyte colony stimulating factor (r-metHuG-CSF) following conventional chemotherapy for small cell lung cancer. 130 previously untreated patients were randomised to receive either r-metHuG-CSF (230 micrograms/m2) or placebo on days 4-17 following CDE (cyclophosphamide, doxorubicin and etoposide) chemotherapy. Over all cycles, 53% of 64 patients on placebo and only 26% of 65 patients on r-metHuG-CSF had at least one experience of neutropenia with fever defined as a neutrophil count less than 1.0 x 10(9)/l and a temperature > or = 38.2 degrees C (P < 0.002). It resulted in a reduction in the requirement for parenteral antibiotics from 58% in placebo patients compared with 37% in the r-metHuG-CSF group (P < 0.02), and a significant reduction in the incidence of infection-related hospitalisation. Chemotherapy doses were reduced by 15% or more at least once in 61% of the placebo group compared with 29% in the r-metHuG-CSF group (P < 0.001). 47% of the patients treated with placebo and 29% of the patients treated with r-metHuG-CSF experienced at least one cycle with a delay of 2 days or more in the administration of chemotherapy (P < 0.04). r-metHuG-CSF was well tolerated. There were no significant differences between the two groups in terms of response or survival.