SUMMARY:Regional cerebral blood flow (rCBF) during internal carotid artery (ICA) occlusion for endarterectomy can be measured without inconvenience using the probe holder illustrated.When mean ipsilateral hemispheric CBF exceeds 20 ml/100 gm/min, an intraluminal bypass is not necessary (63% of patients), except in patients with extensive cerebrovascular disease in whom rCBF should also exceed 20 ml/100 gm/min in all areas. ICA “stump” pressure is falsely high in about 20% of patients, and is therefore not a dependable criterion for selecting patients who need shunting.While intraoperative shunting is capable of restoring pre-occlusion CBF levels, it does not eliminate the risk of intraoperative ischemic neurological deficit of probable embolic origin.