Twelve previously untreated patients with small cell lung carcinoma (SCLC) were treated with r-interferon-gamma (Immuneron, Biogen S.A., Geneva, Switzerland). The planned dose was 1 mg (28 X 10(6) mu)/ms daily for 5 days, followed by 0.5 mg/m2 three times a week for 3 weeks or until progression, whichever was first. Eight patients were fully evaluable, and there were no responses. In four of the eight, the disease remained stable for 1 month, and four progressed before this time. Toxic reactions included pyrexia, headache, and malaise, which were mild to moderate. Ten patients subsequently received conventional chemotherapy, which resulted in three complete and four partial responses. The mean duration of response to chemotherapy was 8 months. It is concluded that r-interferon-gamma, at the dose and schedule used, has no significant clinical activity in small cell lung carcinoma.