Detailed clinical sensory and motor signs were correlated case by case with somatosensory evoked potentials (SEP) in 22 selected patients with a single circumscribed hemisphere lesion. The lesions collectively mapped out a variety of cerebral sites from the anterior frontal to the posterior parietal regions. SEPs were averaged from 8 standard scalp sites with an earlobe reference electrode, so that parietal N20-P27-P45 were differentiated from prerolandic P22-N30 SEP components. SEP wave forms to stimulation on the unaffected side served as the patient's own control.