In 14 patients with severe head injury, the cerebral blood flow (CBF) during mild hypothermia therapy was measured. Their Glasgow Coma Scale scores on admission were 8 or less and the intracranial pressures were greater than 20 mmHg despite conventional therapy. The CBF was measured with two-level stable xenon CT techniques. And in 11 patients, the cerebral metabolic rates for oxygen (CMRO2) was also calculated. All cases were divided into two groups according to the outcome at discharge by using the Glasgow Outcome Scale, good outcome group in 6 and poor outcome one in 8. The values of mean CBF and CMRO2 of each group were 25.6 +/- 6.6 vs 24.4 +/- 6.4 ml/100 g/min and 1.26 +/- 0.45 vs 0.79 +/- 0.31 ml/100 g/ml, respectively. There were no statistically significant differences between both groups. Single CBF measurement during this therapy may not be helpful as a factor of prognosis evaluation in patients with severe head injury.