Introduction: Endothelial barrier dysfunction is associated with many types of vascular diseases (e.g. atherosclerosis, inflammation and ischemia/reperfusion). Endothelial barrier function is mainly regulated by cell-cell adhesions and endothelial contractile machinery. Rho family of GTPases particularly RhoA and Rac1 are the main regulators of both endothelial cell-cell adhesions and contractile machinery. The activity of Rho GTPases is regulated by different mechanisms including by post-translational prenylation. Prenylation of both RhoA and Rac1 is regulated by farnesyltransferase and geranylgeranyltransferase, and dysregulation of their activity may influence the activity of RhoA and Rac1. In the present study, the effect of RhoA and Rac1 prenylation on endothelial permeability was analysed. Methods: The study was performed on isolated human umbilical vein endothelial cells (HUVECs). Endothelial barrier function was analysed by measuring flux of labeled albumin through HUVEC monolayers. RhoA and Rac1 activity was measured by pulldown assay. Thrombin was used as an inflammatory mediator. Results and Conclusion: In this presentation, we will present the data showing how interfering with the activities of farnesyltransferase and geranylgeranyltransferase can differentially affect the activities of Rho GTPases and thus influence endothelial permeability both positively and negatively. Moreover, the data on the influence of statins, which also inhibit protein prenylation, on Rho GTPases and thus endothelial barrier function will be discussed.