Hormones influence renal function by both extrarenal and intrarenal mechanisms. Extrarenal mechanisms include the effects through systemic hemodynamic and neural pathways, whereas intrarenal mechanisms can be largely divided into the effects on intrarenal hemodynamics and those on tubular transport epithelia. Neurohypophysial hormones and the renin-angiotensin system appear to act primarily on systemic and preglomerularvasculature in primitive vertebrates, while direct tubular action appears to have evolved at a later stage of phylogeny. Although aldosterone is an essential hormone for fluid mineral balance in mammals, the action of mineralocorticoids on tubular Na transport has not been established in nonmammalian tetrapods. In bony fishes in hyperosmotic environments, cortisol accelerates active Na extrusion from the gill. In contrast, prolactin is important for maintaining low osmotic water permeability of the transport epithelia in fishes in hypoosmotic media. Thus, both function and site of hormone action appear to have changed during the evolution of vertebrates interacting with changing environments, and in response to the demands from other bodily functions. Furthermore, evolution of interactions, at the cellular level, between systemic and locally formed hormones such as prostaglandins, kinins, and perhaps angiotensin may have developed more elaborate controlling systems of renal handling of solutes and water.