arterial oxygen tension greater than 300 mm Hg (using inspired oxygen fraction of 1.0 and positive end-expiratory pressure 5 cm H2O), and chest radiograph negative for infiltrate or trauma (contusion or pneumothorax). Thirty-seven donors failed to satisfy one of these criteria and seven donors failed to satisfy two of them, yielding 51 criteria denoting marginal status in the 44 donors in the marginal group (group II) as follows: age older than 55 years