Angiotensin III (Ang III) is a bioactive heptapeptide that is formed from the degradation of the Angiotensin II peptide by aminopeptidase A. In peripheral Angiotensin systems, Angiotensin II is the main effector peptide in the systemic circulation, although exogenous Angiotensin III can be as potent as Angiotensin II in, for example, stimulating aldosterone secretion or inhibiting renin release. In the rat brain, Angiotensin III was found to be equipotent with Angiotensin II as a pressor agent or dipsogen and was bound as avidly to the nervous system as Angiotensin II. Angiotensin receptor subtype AT1 has the greater affinity towards Angiotensin II and is also responsive to Angiotensin III, while the AT2 receptor subtype appears to be more sensitive to Angiotensin III but less responsive to Angiotensin II. Angiotensin III enhances blood pressure, vasopressin release and thirst when it is centrally administrated. Angiotensin III infusion increases blood pressure in healthy volunteers and hypertensive patients as well as augments aldosterone release. Although Angiotensin III does not change renal function in humans, it induces natriuresis in AT, receptor-blocked rats likely by binding to AT2 receptors. In addition, in cultured renal cells, this peptide stimulates the expression of many growth factors, proinflammatory mediators, and extracellular matrix proteins.