Central conduction time (CCT) has been monitored in 37 patients undergoing temporary arterial occlusion in aneurysm surgery. 17 patients had internal carotid, 17 had middle cerebral, and 4 had basilar artery occlusion. Internal carotid or middle cerebral artery occlusion lasting less than 12 minutes has not been associated with postoperative morbidity, in any case without appreciable change in CCT after occlusion. Prompt prolongation of CCT was warned the surgeon, but CCT prolongation up to 10 ms could occur without permanent neurological deficit, except in one Grade 4 patient. 10 of 18 patients who lost the N 20 cortical potential showed postoperative neurological deficit, which was promptly recoverable in 7 patients. The speed of loss or recovery of N 20 enabled a patients's prognosis to be predicted. Irrecoverable postoperative deficit is unlikely if the N 20 takes longer than 4 minutes to disappear, to reappears within 20 minutes after recirculation.