Of forty-three consecutive patients with severe adult respiratory distress syndrome (ARDS) treated in the prone position pulmonary function improved significantly in 39 patients during the first 12 h in prone position. Changes were most pronounced in patients with high QS/QT, as well as in patients in the early stages of ARDS. Twenty-eight patients could be weaned from the ventilator, and 22 patients were able to leave the hospital. These results suggest that prone position has an important role in the overall therapeutic approach to ARDS and should be used as early as possible.