Global cerebral oxygenation, perfusion pressure, and expired pCO2 were continuously monitored in 10 adults with acute severe closed head trauma. Cerebral oxygenation was monitored by fiberoptic catheter oximetry, which allowed simultaneous measurements of arterial and jugular bulb oxyhemoglobin saturation. Intracranial pressure levels over 20 mm Hg were recorded several times in all patients, in spite of sedation, muscle paralysis, and profound hyperventilation. Intracranial hypertension was frequently associated with oligemic cerebral hypoxia, identified as abnormally low jugular oxygen saturation in the presence of normal arterial oxygenation. Intracranial hypertension was then managed with intravenous administration of mannitol boluses, which yielded simultaneous decreases in intracranial pressure and increases in cerebral oxygenation to highly statistically significant levels. Monitoring cerebral oxygenation was clinically useful because it allowed identification of impaired cerebral oxygenation even when cerebral perfusion pressure was normal. It is therefore proposed as a new monitoring technique, to supplement conventional monitoring of cerebral perfusion pressure.