Increased endothelial permeability is involved in the pathogenesis of many cardiovascular and pulmonary diseases. Vascular Endothelial growth factor (VEGF) is a permeability-increasing cytokine. At the same time, VEGF is known to have beneficial effect on endothelial cells (EC), increasing their survival. Pulmonary endothelium particularly, may be exposed to higher VEGF concentrations, since the VEGF level is the higher in the lungs than in any other organ. The purpose of this work was to evaluate the effects of VEGF on barrier function and motility of cultured human pulmonary EC. Using transendothelilal resistance measurements as an indicator of permeability, we found that 10 ng/ml VEGF significantly improved barrier properties of cultured human pulmonary artery EC (118.6±0.6% compared to 100% control, p<0.001). In contrast, challenge with 100 ng/ml VEGF decreased endothelial barrier (71.6±1.0 % compared to 100% control, p<0.001) and caused disruption of adherens junctions. VEGF at both concentrations increased cellular migration; however, 10 ng/ml VEGF had a significantly stronger effect. VEGF caused a dose-dependent increase in intracellular Ca²⁺ concentration, however phosphorylation of myosin light chain was detectably elevated only after treatment with 100 ng/ml. In contrast, 10 ng/ml, but not 100 ng/ml VEGF caused significant increase in intracellular cAMP (known barrier-protective stimulus) compared with non-stimulated cells (1096±157 fmol/mg and 610±86 fmol/mg respectively, p<0.024). Y⁵⁷⁶-specific phosphorylation of focal adhesion kinase was also stimulated by 10 ng/ml VEGF. Our data suggest that depending on its concentration, VEGF may cause diverse effects on pulmonary endothelial permeability via different signaling pathways.