Endothelial cells function as a highly regulated barrier between blood and interstitium. They play a central role in the regulation of vascular permeability by controlling the passage of liquid and nutrients as well as the transit of white blood cells (1 ,2 ). The endothelium is involved in the inflammatory response by either secreting cytokines or responding to blood-derived mediators or signals from adjacent cells (3 –6 ). In 1973, Jaffe and coworkers (7 ) first published the culture of endothelial cells isolated from human umbilical veins. Ryan and coworkers (8 ) described, in 1978, the first isolation of pulmonary artery endothelial cells. Porcine endothelial cells have been used to study endothelial permeability in vitro (2 ,10 ,9 ) adhesion (11 ), and blood coagulation (12 ). Since the regulation of endothelial permeability is critical for pulmonary gas exchange, the close vicinity to airway epithelial cells has drawn attention to interactions between both cell types. Here we describe the isolation and culture of pulmonary artery endothelial cells and outline the in vitro measurement of endothelial permeability.