Eleven supine adult patients undergoing general inhalation anesthesia with halothane-nitrous oxide-oxygen and dtubocurarine were studied. In order to determine the effectiveniss of the method to estimate the minute volume by ones height and, to find the merrits of changed tidal volume under the constant minute volume, we observed the changes in PaCO₂, arterial pH, base excess, systolic and diastolic blood pressure and pulse rate during general anesthesia with mechanical ventilation. In this study, there were no significant changes in PaCO₂, arterial pH, base excess, systolic and diastolic blood pressure and pulse rate during mechanical ventilation with the changed tidal volume. Furthermore, we considered that the large tidal volume prevented miliary atelectasis and increasing A-aDO2.