Angiotensin II (AII), the effector octapeptide of the renin-angiotensin system, exerts a multitude of actions, including vascular contraction, aldosterone secretion, catecholamine release, glycogenolysis, and decreased renal filtration. These diverse actions are mediated through AII receptor subtypes present in a variety of target tissues. Molecular cloning studies have identified two major types of mammalian AII receptors, designated AT1 and AT2, which are classified as a typical family of seven transmembrane guanyl nucleotide-binding protein (G-protein) coupled receptors from hydropathy analyses. Mainly, if not all, of the actions of AII are mediated by AT1 that has been well characterized. Recently, AT2 is found to exert growth inhibitory and proapoptotic effects, but its physiological role is still unclear. The molecular mechanism and the physiological importance of signaling pathways via these receptors remain to be elucidated.