A dissociative anesthetic agent, ketamine has bronchodilating property and its bronchodilating effects in asthmatic patients have been apparent since earlier clinical studies. In this study, after anesthetizing patients who did not have any respiratory disease, we administered ketamine to the patients intravenously, and then monitored airway pressure to see the changes in respiratory mechanics indirectly. ASA physical status class 1 and 2 surgical patients who didn't have any respiratory disease were studied. Without premedication, fentanyl 3 mcg/kg, midazolam 0.1 mg/kg, thiopental 3 mg/kg and vecuronium 0.15 mg/kg were injected intravenously consecutively. Ventilation was controlled by face mask with O2-N2O(50%)-isoflurane(<0.5 vo1.%) for 5 minutes with closed circuit anesthetic machine(Physio-Flex). After intubation, anesthesia was maintained with O2-N2O(50%)-isoflurane(<0.5 vol.%) and controlled ventilation was done with tidal volume 9 ml/kg, respiratory rate 11/min and inspiratory flow was constant for each subject. When airway pressure was stabilized, ketamine 4 mg/kg was administered intravenously, Thereafter, for 20 minutes P(peak), P(plateau), P(mean), mean arterial pressure and heart rate were monitored every minute interval. Dynamic compliance, static compliance and resistance of the total respiratory system were calculated by inspiratory pressure method. The result is that ketamine does not produce significant changes in airway pressure, resistance and compliance of total respiratory system. In conclusion, ketamine does not have bronchodilating effect in normal pntients anesthetized with isoflurane of low concentration.