Postoperative ventilatory status was studied in three groups of patients totaling 79: the first group anesthetized with N2O and large doses of d-tubocurare followed by complete reversal with neostigmine, a second with N2O-ether and a third with cyclopropane. Changes in arterial blood gases and inspiratory force were the criteria used.Significant differences among the groups occurred only in the first hour postoperatively: (1) CO2retention in cyclopropane group compared to other groups and (2) less acidosis and higher inspiratory force measurements in female patients receiving curare, when a nerve muscle stimulator was used to define complete reversal of curarization.