Ankaferd Blood Stopper (ABS) is a novel topical hemostatic agent with pleiotropic actions indicated in clinical hemorrhages. Protease-activated receptor 1 (PAR-1) is located in the crossroads of hemostasis, inflammation, infection, apoptosis and tumorigenesis. ABS-induced formation of the protein network with vital erythroid aggregation covers the entire physiological hemostatic process. The aim of this study is to assess the effects of ABS on PAR-1 in the Human Umbilical Vein Endothelial Cells (HUVEC) model, in relation to the "ipopolysaccharides (LPS)-challenge'' to endothelium. For this purpose, ABS 10 mu L and 100 mu L, had been applied to HUVEC within the time periods of 5 minutes (min), 25 min, 50 min, 6 hours (h) and 24 h. The cells have lifted from the plastic surface and adhered to each other during theABSapplication to the HUVECs. After 24 hours the cells returned to normal baseline level. We observed dose-dependent reversible PAR-1 down-regulation mediated by ABS inside the human umbilical vein endothelial cells. ABS-induced sustained PAR-1 down-regulation in the presence of LPS. Those findings indicated that ABS hemostatic agent may act as a topical biological response modifier by acting on PAR-1 at the vascular endothelial and cellular level.