Use of body positioning to improve oxygenation in mechanically ventilated patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) has been well documented. However, neither prone position ventilation nor side lying ventilation has been reported to improve the survival. Whether there is a body position superior to routine supine position or other positions as therapeutic adjunct for ventilated patients with ALI and ARDS? We propose the hypothesis that upright position ventilation may be helpful to improve oxygenation and benefit patients with ALI/ARDS. According to the existing physiologic and pathophysiologic data of upright position investigation, we suppose that improvement of V/Q matching, increased functional residual capacity, alveolar recruitment, accelerated diaphragm recovery, early gastric emptying and enteric feeding may be a potential protect mechanism of upright position ventilation. Whether this can be translated into improvement in patient outcome should be further tested in clinical trial.