Atrial natriuretic peptide (ANP) and its receptors have been identified in amphibian tissues. Granules containing natriuretic peptides are present in the atria and ventricules of frogs and toads. The role of ANP in amphibian physiology is not well established although a vasorelaxant effect of toad heart extracts and synthetic peptide have been characterised in contracted toad and frog vessels. A vasorelaxant effect on non-contracted toad, aorta has been described when the vessel is previously sensitized with angiotensin II. Frog heart extracts produce natriuresis in the rat and in the isolated toad skin it inhibits the hydrosmotic response to angiotensin II and the natriferic and hydrosmotic response to arginine vasotocin. Receptors for ANP are present in the central nervous system of the clawded toad in areas related to water and electrolyte metabolism.