The use of routine radioisotope scanning to screen for subclinical metastatic disease in the initial staging of bronchogenic carcinoma was studied. To define the value of scans, liver, brain, and bone scans were studied prospectively in 111 patients and retrospectively in 114 patients. Among patients with clinical findings suggesting metastatic disease, 14.4 per cent of the liver scans, 12.3 per cent of the brain scans, and 35.7 per cent of the bone scans were positive. All patients free of clinical findings had negative liver and brain scans. Positive bone scans occurred in 8 per cent of the patients without clinical abnormalities. True-positive bone scans occurred in less than 4 per cent of the patients free of clinical abnormalities. The clinical findings noted in the patients pointed to the organ involved in only 76 per cent of the abnormal liver scans, 62 per cent of the abnormal brain scans, and 75 per cent of the abnormal bone scans. Clinical findings associated with positive liver and brain scans were multiple and significant, whereas findings with the positive bone scans could be few or subtle. Routine scanning failed to identify a significant number of patients with clinically unsuspected metastatic disease. Liver, brain, and bone scanning is indicated only in patients suspected of having metastatic disease.