BACKGROUND: Univent tube(endotracheal tube with a movable blocker), introduced by Inoue et al in 1982, has properties to overcome the disadvantages of double lumen endotracheal tube for one lung anesthesia. This study was performed to evaluate the effectiveness of Univent tube for one lung ventilation. METHODS: Univent tube was inserted to the patients for open thoracic surgery and positioned to the side of bronchus under the guidance of fiberoptic bronchoscope that was scheduled to lung collapse. One lung anesthesia was performed with the inflation of cuff of blocker. Each case was anaylzed with respect to ease or difficulty of positioning of blocker, tube displacement, efficacy of lung collapse and adequacy of single lung ventilation. RESULTS: In the 69 patients out of 80 patients, adequate positioning was performed by first trial. In the two patients, insertion of bronchial blocker was failed that resulted in replacement with a double lumen tube. Observed disadvantages were delayed deflation(10 patients) of affected lung and displacement of bronchial cuff into the main tracheal lumen during position change or surgical manipulation(7 patients). CONCLUSIONS: Univent tube is useful for one lung anesthesia but there are several distinct limitaitons in the safe use.