Thirty-one patients with histologically proven small cell lung cancer were treated with cyclophosphamide 1 g m-2 and etoposide (VP16-213) 125 mg m-2 both intravenously on day 1 followed by etoposide 250 mg m-2 orally on days 2-3 for a maximum of six courses at 3 weekly intervals. Fourteen patients had limited and 17 patients had extensive disease. Twenty-five patients were evaluable for response. Objective response was observed in 18 patients (58%) with 6 (19%) complete and 12 (39%) partial responses. Median survival of the entire group of patients was 30 weeks. There was significant survival benefit among the responders (P less than 0.005) when compared with non-responders. One patient (3.3%) developed grade 4 while 60% of patients developed grade 1-2 haematological toxicity. Other side effects were relatively mild. We conclude that combination cyclophosphamide and etoposide was active in small cell lung cancer and relatively well tolerated.