Acute lung injury (ALI) and its more severe form, adult respiratory distress (ARD), is a devastating clinical syndrome of sudden lung inflammation that results in severe edema and hypoxemia and requires care in the intensive care unit. Mortality is between 30-40% in controlled settings. To date, no single drug has proven effective for improving mortality in ALI/ARDS despite many large and small clinical trials. The objective of the Clinical Research Network (ARDSNet) is to develop and conduct clinical research trials to prevent, treat, and improve the outcome of patients with acute lung injury, acute respiratory distress syndrome, and possibly other related critical illnesses.