The changes of cerebral blood flow velocity, pulsatility index and resistance index were studied during Enflurane-N2O-O2 anesthesia according to the change of end tidal carbon dioxide tension in 14 gynecologic surgical patients. From the both middle cerebral artery, mean blood flow velocity, resistance index and pulsatility index were checked with transcranial doppler before anesthesia with room air respiration and during anesthesia with controlled ventilation. The anesthesia was controlled with 2.0±0.5% Enflurane and 3 liter/min. of nitrous oxide and 2 liter/min. of oxygen. The end tidal CO2 tension was controlled by change of respiratory rate and tidal volume from 30 mmHg to 40 mmHg during anesthesia. Mean blood flow velocity, resistance index, and pulsatility index of middle cerebral artery were compared between unanesthetized room air respirated patient and anesthetized patient. The result were as follows : 1. There were no differences of systolic, diastolic, mean blood flow velocity, resistance index and pulsatility index between right and left middle cerebral artery. 2. The mean blood flow velocity was significantly increased but the pulsatility index and resistance index was decreased during anesthesia compare to preanesthetic values. This may be due to the effect of anesthetics. 3. During steady state of anesthesia the mean blood flow velacity was increased and the pulsatility index and resistance index was decreased according to the change of ETCO2 With this result we can say the effect of carbon dioxide tension to the cerebral blood flow velocity was maintained during Enflurane-N2O-O2 anesthesia, but the flow was also affected by the anesthetics itself.