Fifty-seven patients with histologically proven small cell lung carcinoma were prospectively evaluated for signs of brain metastasis by neurological examination and computerized tomographic (CT) brain scanning. The reliability of demonstrating brain metastases by means of neurological examination was compared with that of CT. Three (5%) patients, two with cerebrovascular infarcts and one with leptomeningeal metastases, were excluded from the study. Four (7%) patients, all with extensive disease, showed neurological symptoms and signs of brain metastases, which were confirmed in three cases by brain CT. The fourth patient had neurological symptoms and signs pointing to cerebral metastasis, but no sign of this was detected on CT at the time of diagnosis. However, six months later, after completion of chemotherapy, CT revealed signs of brain metastasis. The other fifty neurologically asymptomatic patients had no brain metastases on CT. This clinical study suggests that routine CT of the brain is not useful in neurologically asymptomatic patients with small cell lung carcinoma.