Cerebral blood flow (DSC) and oxygen consumption were measured in a series of patients in the acute phase of severe brain injury, and the results analyzed as a function of the level of cerebral dysfunction determined clinically. The most frequent modifications were increased cerebral blood flow and reduced oxygen consumption, whatever the degree of dysfunction. Hemodynamic data has no prognostic value whereas oxygen consumption results are more valid. Increased cerebral blood flow is noted constantly in patients at a level of mesencephalic dysfunction. Reduced O2 consumption associated with increased blood flow is the result of a disturbance in the blood flow-metabolism ratio and could be due to cerebral vasodilatation. This great increase in cerebral vasodilatation observed in cerebral dysfunction syndromes is in favour of the existence of a central neurogenic system in the brain stem regulating cerebral blood circulation.