From November 1976 to November 1978, the Southwest Oncology Group treated 254 patients with extensive (metastatic) small cell carcinoma of the lung with combination chemotherapy and radiotherapy with and without BCG immunotherapy. Patients receiving BCG achieved a response rate of 50% versus those patients not receiving BCG of 46% (P = .704). Response duration was 20 weeks for the BCG arms and 23 weeks for the no-BCG arms; survival was 28 weeks for the BCG arms versus 29 weeks for the no-BCG arms. An adverse effect in patients surviving more than one year was detected; those continuing to receive BCG had significantly shorter survival, 60 weeks versus 85 weeks (P = .019). Toxicities of the programs were not affected by the addition of BCG immunotherapy. It appears that BCG immunotherapy has no beneficial effect on response rate or duration of response in programs using chemotherapy and radiotherapy for control of metastatic small cell carcinoma of the lung. In addition, because of the adverse effect on long-term survival, we do not recommend the addition of BCG immunotherapy as a treatment modality in this tumor type.