Recent data demonstrate that in addition to its conduit function, the blood vessel is an active synthetic and secretory organ containing several autocrine and paracrine systems that are involved with the local regulation of its own function. The endothelium plays a pivotal role in modulating the balance between thrombogenesis and thrombolysis. In addition, it secretes vasorelaxant and vasoconstrictive substances, growth factors and inflammatory mediators that exert paracrine influences on vascular myocyte function. The vascular myocyte also expresses autocrine substances which influence its own function. The autocrine systems include angiotensin, prostaglandins, platelet-derived growth factor, insulin-like growth factor and heparin. These local factors exert modulatory influences on myocyte contractility and growth. It is conceivable that genetic or acquired abnormalities of one or several of these check and balance systems can result in increased vascular tone, generalized vascular hypertrophy or hyperplasia, or a combination, and contribute to the pathogenesis of hypertension. These autocrine-paracrine systems may be important targets for antihypertensive drug development.