Surface tension(in terms of hysteresis), lecithin content, PaO2 and lung water content of both bronchial irrigation fluid and lung homogenates were determined after severe inhalation injury in rabbits. In accompany with the decrease of PaO2 and increase of lung water content, there was a remarkable dropping of pulmonary surfactant content as illustrated by progressive increase of surface tension and decrease of lecithin content in both bronchial irrigation fluid and lung homogenate. It was proposed that dropping of pulmonary surfactant played an important role in the pathogenesis of pulmonary edema after inhalation injury. Therefore, successive determinations of lecithin content or and surface tension of bronchial irrigation fluid might serve as an early diagnosis as well as a pro-gnostis aid in severe inhalation injuries.