The pulmonary artery carries deoxygenated blood from the heart to the lungs. Similar to other vascular endothelial cells, human pulmonary artery endothelial cells (PAEC) modulate coagulation and fibrinolysis by producing activators and inhibitors of both processes. In addition, PAEC produce mediators that influence the adhesion and aggregation of blood platelets. PAEC also control vascular tone by synthesizing and processing vasoactive molecules. PAEC further interact with mesenchymal cells and regulate inflammatory events. Such functions of PAEC play roles in acute lung injury, pulmonary hypertension, edema, embolism, pulmonary artery aneurysm and chronic obstructive lung disease. HPAEC will provide an in vitro model in the pathophysiological studies of vascular diseases; such pulmonary arterial hypertension. They are also useful tools to stablish in vitro disease models for High Throughput and High Content Screening.