Monitoring of multichannel somatosensory evoked potentials (SEPs) has been performed in 40 cases of carotid endarterectomy (CEA). SEPs were obtained after median nerve stimulation at wrist, recording from 2nd cervical and from the scalp parietal (ipsi- and contralateral) and central (contralateral) positions. The reduction of CBF due to clamping of the carotid artery provoked SEP abnormalities in 10 of the 40 cases. None of the 30 patients with unmodified SEPs developed post-surgical neurological sequelae. SEP alterations were characterized exclusively by amplitude decrements and latency increases of the cortical components, the subcortical ones being unaffected. In 5 of these patients, SEPs returned to normal values before the end of the intervention and no neurological deficit was observed on awakening. In the remaining 5 cases SEPs retained their abnormalities and patients developed post-surgery neurological sequelae (4 immediately, 1 the day after). SEP alterations affected parietal and central components to a similar extent; however, in a few cases cerebral blood flow deficits provoked by carotid clamping modified differently the central P22 and the parietal N20-P25 waves. Comparisons with stump (back) pressure in the carotid artery revealed a higher sensitivity of the SEP technique in detecting vascularization problems due to carotid clamping. The time course of the appearance of SEP abnormalities seems to discriminate alterations secondary to collateral revascularization from those determined by embolization.