A method is described which utilizes the recording of somatosensory evoked responses and cortical stimulation to localize the sensorimotor area under general anesthesia. It has been used in 31 patients who had lesions located in or near the somatosensory or motor gyri. Twenty-six of these patients had a tumor, and the remaining five had a tuberculoma, cysticercoid cyst, thrombosed arteriovenous malformation, cystic infarct, and astrocytic proliferation, respectively. Case histories of selected patients are briefly reported to demonstrate how the method can be used to improve the safety of surgical excisions in the sensorimotor area. The neurological results are discussed in relation to recent physiological studies, demonstrating multiple and spatially separate, sensory and motor representations of the body in the somatosensory and motor gyri.