The effects of midazolam, 0.2 mg/kg body weight on cerebral blood flow, cerebral O2 consumption and brain metabolism were studied in 8 patients scheduled for intracranial aneurysm surgery. All patients were anesthetized with fentanyl and N2O; arterial p[partial pressure]CO2 and pO2 were maintained within the normal range by controlled ventilation. Midazolam produced minimal effects on the general circulation. Cerebral blood-flow decreased .apprx. 11% while cerebral O2 consumption essentially remained unchanged. Cerebral perfusion pressure slightly decreased due to a reduction in mean aortic pressure. In 3 patients with elevated intracranial pressure midazolam decreased intracranial pressure significantly while there was no change in the other patients. Midazolam is of no harm in patients with intracranial aneurysms. This rapidly acting drug in addition to other measures might be of some benefit in patients with elevated intracranial pressure when immediate reduction of cerebral blood volume is desired.