Abstract: This paper reported the results of the determination of PaO₂, A-aDO₂ and·Qs/·Qt in patients undergoing thoracic surgery, using double-lumen endobronchial intubation. 10 patients with normal pulmonary function were performed five different ventlated maneuvers. After the respiratory pattern shifting to one-lung ventilation, PaO₂ was reduced from 340.0 to 127.8, A-aDO₂ and ·Qs/·Qt were increased significantly. While differential lung ventilation, all parameters were improved approximating to two-lung ventilated levels. Five patients with moderate pulmonary insufficiency couldn't tolerate one-lung ventilation. When differential lung ventilaton was used instead, PaO₂ returned to two-lung ventilated level. It suggests that differential lung ventilation not only preserves all the adventages of one-lung ventilation, but also decreases transpulmonary shunt improving pulmonary oxygenation.