Prone position and recruitment maneuvers (RM) are proposed as adjuncts to mechanical ventilation to open up the lung and keep it open. We studied the oxygenation response to a RM (composed of a 30-s sustained inflation at 60 cm H2O airway pressure) performed in prone and supine positions in dogs after oleic acid-induced lung injury using an inspired O-2 fraction of 0.60. In one group (n = 6) first supine then prone positions were examined after a RM at 8 cm H2O and 15 cm H2O of positive end-expiratory pressure (PEEP). In the second group (n = 6) the sequence of positions was reversed. Prone positioning after supine position always improved oxygenation, whereas the decrement in Pa-O2 was relatively small when dogs were returned to the supine position. Oxygenation improved in both groups after a RM, and the improvement was sustained (after 15 min) in the prone position at 8 cm H2O of PEEP, but 15 cm H2O of PEEP was required in supine position. Our results suggest that a RM improves oxygenation more effectively with a decreased PEEP requirement for the preservation of the oxygenation response in prone compared with supine position.