Cerebral blood flow velocities in the middle cerebral arteries were measured using transcranial Doppler in 12 patients with conditions that ultimately resulted in brain death. All patients had sustained closed head injury, gunshot wounds to the head, or spontaneous intracerebral hemorrhages. When clinical criteria for brain death were met, a characteristic pattern was found with transcranial Doppler. This pattern consisted of reverberating flow, with forward flow in systole and retrograde flow in diastole. When this pattern was seen, there was arrest of cerebral flow, as measured by radionuclide scanning using technetium, in all patients studied. Transcranial Doppler is a useful technique for easily assessing the arrest of the cerebral circulation.