The aim of this prospective study was to investigate the feasibility of increasing the dose intensity of chemotherapy in patients with small cell lung cancer (SCLC) by using recombinant human granulocyte colony-stimulating factor (r-metHuG-CSF). Seventeen previously untreated patients (11 male, 6 female) were treated with ifosfamide (5.0 g/m2) and epirubicin (80 mg/m2) in two successive cohorts. Eight patients received chemotherapy every 2 weeks and r-metHuG-CSF 5 microg/kg given subcutaneously daily for 10 days (cohort A), and nine patients received chemotherapy at 10-day intervals with r-metHuG-CSF 5 microg/kg subcutaneously given daily for 7 days (cohort B). The relative dose intensity compared with the conventional 3-weekly regimen was 1.5 and 2.1 for cohorts A and B, respectively. Neutropenia-associated fever complicated two and five treatment courses in cohorts A and B, respectively. There were five episodes of grade 3/4 thrombocytopenia. There were no treatment delays in cohort A and one cycle was delayed in cohort B. One patient from each cohort was withdrawn due to toxicity. Grade 3/4 non-haematological toxicity, other than alopecia, was not observed. This study confirms that it is feasible to increase the relative dose intensity of ifosfamide and epirubicin in patients with SCLC to 2.1 by using r-metHuG-CSF and shortening the interval between treatment cycles.