A total of 610 patients with small cell lung cancer were entered into a randomised trial designed to assess the effect of duration of initial chemotherapy on survival. Patients were randomised to receive either four or eight courses of cytotoxic chemotherapy with cyclophosphamide, vincristine and etoposide and also randomised to receive, on disease progression, either second line chemotherapy (methotrexate and doxorubicin) or symptomatic treatment only. In the whole study 196 (32.1%) had limited disease and 414 (67.9%) extensive disease. During initial chemotherapy the response rate (complete and partial responses) after four courses of treatment was 61% with no significant increase in patients receiving eight courses (63%). In those randomised to receive relapse chemotherapy the response rate was improved slightly for those who had originally received four courses of chemotherapy (25.6%) over those receiving eight (18.7%). The overall results show that of the four possible treatment randomizations, four courses of chemotherapy alone is inferior in terms of overall survival (30 weeks median survival) to the other three treatment options (39 weeks median survival, P less than 0.01). In patients responding to initial chemotherapy the disadvantage of four courses of chemotherapy alone was apparent (median survival of 40 weeks versus 49 weeks, P = 0.003) but not if drug treatment was given on relapse. The study shows that limiting treatment to four courses of chemotherapy alone is associated with inferior survival, but this is not the case if chemotherapy is given at relapse.