The renin-angiotensin system is intricately involved in the homeostasis of peripheral vacular resistance as well as volume and electrolyte composition of body fluids (for reviews before 1966 see 63, 391, 413,474; after 1966 see 278, 359, 382, 392, 394, 425). Until recently, the proteolytic enzyme renin and the octapeptide angiotensin II (AII) have been the focal points for most studies that have addressed the physiologic and/or pathophysiologic significance of this complex system. Angiotensin II is a very potent peptide with a vast spectrum of biologic activities. Advances in metho ology for peptide synthesis and the demonstration of the receptor blocking properties of analogues of AI1 with aliphatic COOH-terminal residues have been the basis for numerous new findings and observations. The availability of converting enzyme inhibitors has also been an impetus for studies of the renin-angiotensin system and in particular studies with angiotensin I (AI). Recent studies have suggested that this decapeptide, AI, may have significant biologic activity in the kidney and within primitive structures of the nervous system (72, 73, 405, 524). The heptapeptide homologue [des-Aspl] AII also has received a great deal of attention as a potential steroidogenic factor in the adrenal zona glomerulosa (39, 6591, 451). To discuss the impact of these and other observations on our basic