As measured in decerebrate cats, inspiratory air flow resistance initially reduces the tidal volume and frequency of respiration. The reduction in tidal volume is aggravated by pentobarbital, nitrous oxide, or ether. If the flow resistance persists, there is a gradual recovery in the volume of ventilation, but even in the unanesthetized state this is not complete at the end of five minutes. Ventilation is reduced with increased airway resistance in spite of augmented muscular activity. The reduction of ventilation is proportional to the magnitude of the resistance.