Balloon occlusion pulmonary angiography was used to assess the frequency of pulmonary vascular thrombosis in five patients suffering from ARDS of diverse causes. Pulmonary hypertension, elevated pulmonary vascular resistance and disseminated intravascular coagulation were observed in all patients. Pulmonary artery filling defects (PAFD) were found in four of five patients. The results suggest that PAFD can be detected in a large proportion of patients in ARDS. It was therefore speculated that the detection of PAFD is a sign of severe lung injury. Urokinase, heparin and protease inhibitor were infused to test the potential reversibility of pulmonary vascular thrombosis in four patients. After infusion, we found angiographic evidence of clearing of obstruction in arteries in three of four patients. We conclude that anticoagulant-antithrombotic therapy can improve hemodynamics in ARDS-associated pulmonary vascular thrombosis.