We designed this study to determine whether standard ventilator settings applied on the day ARDS is identified (Day 0) or 24 hours (Day 1) later: (1) would have an impact on the reclassification of patients into ALI or ARDS, and (2) would identify groups with different clinical outcomes. Our hypothesis was that the assessment of PaO2/FiO2 on standard ventilator settings 24 hours after patients originally met the AECC definition of ARDS would identify patients with established ARDS (persisting over 24 h) from others with different degrees of lung injury. If this hypothesis is supported, it would suggest that patients with a better outcome could have been preferentially entered into one group of previously conducted clinical trials, resulting in a viable therapy being proved useless or useless therapy proven viable.