Endothelium has both a protective and a very complex para-, endo- and autocrine functions. Vascular tone is determined as a balance between the production of vasodilating and vasoconstrictive substances. Among the most important vasodilators are nitric oxide (NO), PGI2, endothelial-derived hyperpolarizing factor (EDHF), adenosine and others, among the most important vasoconstrictors, endothelin-1 and angiotensin-2. Therapeutic goal of improving endothelial secretory function should be maximizing production of vasodilators and minimizing production of vasoconstrictors. Improvement of endothelial function can be achieved most effectively by following a healthy lifestyle (changing the diet to a Mediterranean type, sufficient physical activity, weight reduction and smoking cessation) and by initiating the treatment with ACE inhibitors and statins, when indicated. Large number of trials have shown that all of these interventions improve the prognosis of patients and a part of this effect may be mediated by improving endothelial dysfunction. Key words: endothelial dysfunction - endothelium - hypertension.