Elevated levels of nitric oxide (NO) are detectable in the exhaled breath of patients suffering from a number of inflammatory lung diseases. We hypothesized that NO would be detectable in the exhaled air of patients with the acute respiratory distress syndrome (ARDS) undergoing mechanical ventilation and that the concentration would be greater than that from a control group of ventilated subjects. The concentration of NO in the lower airways of 13 patients with ARDS and 18 patients anesthetized and ventilated prior to cardiac surgery was measured by chemiluminescence. The NO concentration was 1.13 +/- 0.36 (mean +/- SEM) parts per billion (ppb) in the ARDS group and 5.5 +/- 0.8 ppb in the control group (2 p < 0.0001). NO is detectable in the exhaled air of patients with ARDS and is at a lower concentration than in control subjects.