Endothelium is more and more likely to be considered as the biggest endocrine gland of human body. According to number, mass, surface of endothelial cells in adolescent, ability of synthesis and release of substances with multidirectional biological functions, endothelium should be treated as integral organ. Endothelial cells form barrier between blood and smooth muscle cells, playing crucial role in regulation of vasomotorics, hemostasis, angiogenesis, inflammatory processes and immunology. Strategic localization places endothelial cells in very first line of contact with cells and substances migrating from blood to tissue. Endothelium, via large number of yet not in-depth known mechanisms, can react to changes in pressure, blood flow and gas concentration. It is an easy stimulated and fast reacting structure, capable of quick activation and change in its own function. Mechanical damage, or loss of functional integrity, disturbs homeostasis of microenvironment, leading to development of pathological states, like hypertension, atherogenesis, thrombotic lesions, disturbances in perfusion of tissue and organs. The aim of this study was rewiev of the role of endothelial cells in vasomotorics, hemostasis, tumorgenesis and angiogenesis.