An automatic, data-driven blood gas monitoring program calculated the arterial/Alveolar (a/A) oxygen partial pressure ratio for all arterial blood gas samples drawn between April 1987 and February 1988 (total approximately 40,000). Patients with an a/A ratio ≤0.2 were examined to determine if they had Adult Respiratory Distress Syndrome (ARDS). To determine if ARDS was linked to the inspired oxygen fraction (FiO2) or to pressure exposure, a computer exposure monitoring program evaluated each patient's total exposure to FiO2, positive end expiratory pressure (PEEP), and peak inspiratory pressure (Peak), from the date of hospital admission until 24 hours after the a/A ratio was ≤0.2. Of the approximately 6,000 patients originally screened, 372 (p 2 ≥60% (22.2% vs. 59.9%), PEEP ≥10 cm H2O (25.7% vs. 50.1%) and Peak ≥55 cm H2O (2.2% vs. 7.2%), with no statistical difference in their Acute Physiologic Score (APS) (14.5 vs. 13.5). Observations made using the HELP computer system as a monitor, suggest that oxygen and pressure exposure are associated with the development of ARDS.