Between March 1986 and May 1988, the Southwest Oncology Group enrolled 58 previously untreated patients with limited small-cell lung cancer on a treatment program that administered high-dose cyclophosphamide (150 mg/kg) as late intensification. Treatment consisted of induction chemo-radiotherapy, (weeks 1 to 11), consolidation chemotherapy (weeks 11 to 18), and intensification (week 18). Median age was 61.5 years. Eighty-nine percent of patients had a Southwest Oncology Group (SWOG) performance status of 0-1. Twenty-one patients completed all prescribed treatments. There were seven treatment-related deaths, four as a result of intensification. Fifty-six patients are available for response analysis. Thirty-two patients achieved a complete remission (CR) (57%) and fifteen achieved a partial remission (PR) (26%). Median survival for all patients is 11.1 months. Among the 21 patients who received intensification, nine remain alive in a CR with a median survival of 27 months. This sequence of treatments was not associated with a survival advantage for the group as a whole, possibly because of the toxicity of induction and consolidation treatment and the delayed administration of high-dose cyclophosphamide.