To exploit possible dose-response and combination drug synergism, 20 previously untreated patients with extensive-stage small-cell lung cancer (SCLC) received one or two courses of high-dose induction chemotherapy consisting of cyclophosphamide (100 mg/kg), etoposide (1,200 mg/m2), and cisplatin (120 mg/m2) (HDCEP). HDCEP was followed by four cycles of standard-dose cyclophosphamide (1,000 mg/m2), doxorubicin (40 mg/m2), and vincristine (1.4 mg/m2) (CAV). Response was determined after HDCEP and following CAV. Reevaluation included repeat bronchoscopy and chest computerized tomography (CT), as well as repetition of all initially abnormal studies. All patients were evaluable for response and toxicity. Overall response to HDCEP was 90%, with a complete response (CR) rate of 65% (95% confidence limits, 44% to 86%) and a partial response (PR) rate of 25% (95% confidence limits, 6% to 44%). All patients either maintained or improved their initial response while receiving CAV. Median duration of response was 6 months (range, 2 to 12 months) and median survival was 9.5 + months (range, 2 to 21 + months). All 37 courses of HDCEP were associated with leukopenia (less than 1,000/microL), 92% with thrombocytopenia (less than 20,000/microL), and 84% with fever of greater than 38.5 degrees C. Additional toxicities included bacteremia (24%), nausea and emesis (59%), mucositis (57%), diarrhea (38%), and hemorrhagic cystitis (5%). There were two treatment-related deaths due to infection. A third patient died 4 months after completing HDCEP with pulmonary fibrosis. Although response duration and median survival were not improved, HDCEP produced a high CR rate in ambulatory patients with extensive-stage SCLC.