Endothelins are substances produced by the endothelium that have a vasoconstrictive effect. From a functional point of view, endothelins can be considered the physiological antagonists of various different substances that have a vasodilatative effect, and they contribute, together with the latter, towards cotrolling the vascular tone. Interest in these sustances has further increased following the discovery of their involvement in various different diseases in man. This review considers first of all the structure, biosynthesis and activity of endothelins. Then the role of these substances in hypertension and other diseases, including atherosclerosis, cerebrovascular diseases, peripheral vascular disease and other pathological conditions linked with hypertension is discussed. In the conclusion, the widespread nature of the action of endothelins in many tissues and in a wide range of pathological conditions is mentioned.