['The primary objective of this study was to test the hypothesis that the degree of systemic endothelial activation, as measured by the release of von Willebrand factor antigen into the circulation and pulmonary edema fluid, is an important determinant of outcome from acute lung injury and acute respiratory distress syndrome.', 'Observational study.', 'Intensive care unit patients in a tertiary university hospital and a university-affiliated city hospital.', 'Fifty-one intubated, mechanically ventilated intensive care unit patients with acute lung injury or acute respiratory distress syndrome as defined by the North American European Consensus Conference definitions.', 'Undiluted pulmonary edema fluid and plasma were collected within 1 hr of endotracheal intubation in all patients.', 'von Willebrand factor antigen concentrations and protein concentration were measured in pulmonary edema fluid and in plasma.', 'At the time of intubation, median plasma von Willebrand factor antigen was 251%, two-fold higher than the median pulmonary edema fluid von Willebrand factor antigen of 130%. Median edema fluid and plasma von Willebrand factor antigen concentrations were significantly higher in patients who did not survive hospitalization. Plasma von Willebrand factor antigen was also higher in those patients who had a longer duration of mechanical ventilation (as measured by ventilator-free days). Plasma von Willebrand factor antigen was also significantly higher in patients with sepsis and two or more organ system failures. According to stepwise logistic regression analysis, plasma von Willebrand factor antigen was independently associated with in hospital death. The positive predictive value for death if the plasma von Willebrand factor antigen concentration was >450% was 83%. A plasma von Willebrand factor antigen concentration of >450% previously has been shown to predict the development of acute respiratory distress syndrome.'] Is von Willebrand factor antigen an independent marker of poor outcome in patients with early acute lung injury?