Low tidal volume (4–8 mL/kg) during mechanical ventilation in adult respiratory distress syndrome is the standard of care. However, there are questions regarding the approach to setting positive end-expiratory pressure and the use of recruitment maneuvers in patients with adult respiratory distress syndrome. Animal data and preliminary patient data suggest that lung recruitment maneuvers can markedly improve arterial oxygen tension (PaO2). Prone positioning has also become established a method of recruiting lung and improving PaO2in those with adult respiratory distress syndrome. The data suggest that recruitment maneuvers in the prone position are most effective in improving PaO2and that the positive end-expiratory pressure level required to sustain the improved PaO2is less in the prone position than in the supine position.