The effect of local intratracheal, intrabronchial, and intravenous application of histamine, has been studied in dogs. Control studies are also carried out with saline. There is an increase in intrathoracic pressure per 100 ml of tidal volume due to locally applied histamine. This change is considered as the measure of bronchoconstriction. There is also a significant change in the bronchial sensitivity to acetylcholine inhalation. The intravenous application of the same quantity of histamine produces very little change in the bronchial sensitivity though it has produced strong and prolonged circulatory effect and even transitory respiratory arrest. The application of saline produces no change. It is concluded that the local chemical stimulus can sensitize the whole respiratory system and produces greater bronchconstriction involving some reflex path.