From June 1979 through April 1982, we treated 35 patients with limited small cell carcinoma on an intensive chemo-radio-immunotherapy regimen, consisting of induction with cyclophosphamide, doxorubicin, and vincristine, alternately cycled with VP-16 and cisplatin. Patients were stratified by performance status and randomized to thymosin, fraction V, or no thymosin. Induction was followed by consolidation, consisting of prophylactic whole-brain radiotherapy and multifield radiotherapy to the primary and mediastinum with cyclophosphamide and vincristine. Patients who were complete responders (CRs) postconsolidation resumed maintenance immediately. Patients were followed from 1 to 3.8 years (median, 2.2 years) at the time of analysis. After induction, 35% (12/34) had become CRs; after consolidation radiotherapy, an additional 10/34 became CRs for a total CR rate of 65% (22/34). There were only 9/34 local failures (26%), of which all but one were impatients who had not become CRs. A prolonged median survival (21 months) has been obtained in patients with limited small cell carcinoma of lung treated with an intensive combined modality regimen. At 1 year, survival is 83%; at 2 years, 46%. There is a 33% long-term survival (greater than 3 years). There is no difference in survival or recurrence rate between patients treated with or without thymosin.