Rational and Background: Recruitment maneuvers (RMs) have beenwidely investigated and several reports have demonstrated beneficial effects onoxygenation and lung mechanics, on the contrary other reports have found nooxygenation improvement with such maneuvers.Objective: To compare recruitment in ARDS patients to patients with thesame lung injury ventilated in the prone position (since proning provides somesort of physiological recruitment.Patients and Methods: Thirty patients were enrolled. Mechanicalventilation was provided using the volume controlled mode. In the CPAPgroup, a CPAP recruitment maneuver of 40cmH2O/40s was applied and thenswitched to baseline ventilatory settings; except for PEEP set to 20cmH2O.FiO2 was decreased to maintain PaO2 70-100mmHg. PEEP was decreased insteps of 2 cmH2O until PaO2 dropped 10% from best PaO2 achieved. AnotherRM was performed & PEEP was set at the level above derecruitment for 6hours. In the Prone Group, patients were placed in the prone position; baselinemechanical ventilation was delivered except for PEEP increased to 20cmH2O,FiO2 decreased to maintain PaO2 70-100mmHg & maintained. PEEP wasdecreased in steps of 2cmH2O until derecruitment then PEEP was increased tothe previous level for 6 hours.Results: There were no significant hemodynamic disturbances. Arterialoxygen tension significantly increased within both groups throughout thestudy. Arterial Carbon dioxide levels didn’t change within and between thetwo groups. PaO2/FiO2 ratio increased in both groups but only significantly inthe CPAP group. Peak, Plateau and Mean airway pressures decreasedsignificantly only in the Prone group Total Static lung compliance significantlyincreased within both groups.Conclusions: According to our results we conclude that Prone Positionmight offer better improvement in respiratory mechanics than CPAP