Disturbance of cerebral vasomotor regulation has been shown to be associated with the severity of traumatic brain injury (TBI). The transient hyperaemic response (THR) test is a test of the pressure autoregulatory response in terms of cerebral blood flow velocity after a brief carotid artery compression. Correlating with the test of cerebral vascular reactivity (CVR) to carbon dioxide by means of passive hyperventilation suggested that the THR test is a simple clinical test for the assessment of cerebral haemodynamic status in head-injured patients.