Since 1971, 66 patients with small cell carcinoma of the lung--32 with limited and 34 with disseminated disease--have received irradiation to the primary tumor. There were 20 local failures, 90% of which were apparent within 30 weeks of the start of irradiation. Patients were treated with local irradiation only (32), irradiation plus combination chemotherapy (25), or local plus total body irradiation (9). With local irradiation alone, tumor control increased with increasing biologic dose. When chemotherapy or total body irradiation was added, doses of irradiation that were otherwise insufficient for local control proved to be effective.