OBJECTIVE Transcranial Doppler ultrasonography has been reported to reflect changes in cerebral blood flow (CBF) with the use of radioactive tracer techniques, which are weighted to measure primarily cortical structures. We tested the hypothesis that changes in transcranial Doppler ultrasonography would reflect changes in CBF in the middle cerebral artery vascular territory with the use of stable xenon-enhanced CT to assess CBF during carotid occlusion. METHODS Thirty-one conscious patients underwent balloon test occlusion of the internal carotid artery and transcranial Doppler ultrasonography and xenon-enhanced CT assessment of blood flow velocity and CBF, respectively, of the middle cerebral artery and its distribution during balloon test occlusion. RESULTS A significant correlation was seen between the change in CBF and the change in blood flow velocity for both brain levels at which CBF was determined (P < .0001). The average change in blood flow velocity was -13.4%, and the change in CBF was -15.1% and -17.7% at the two anatomic levels examined. CONCLUSIONS The data indicate that changes in blood flow velocity generally reflect changes in CBF throughout the middle cerebral artery vascular territory with abrupt occlusion of the internal carotid artery in unanesthetized humans.