It is a great pleasure for me to participate in honoring my mentor, Dr. Donald W. Seldin. When I began my fellowship in Dailas in 1967, the field of renal physiology was booming. Laboratories all over the world were beginning to unravel the puzzle of sodium handling by the nephron and Seldin was one of the main catalysts. From this intellectual experience in Dallas, I spent the next decade or so studying the renal circulation, its effect on sodium transport, and various humoral factors that play a role in the regulation of renal resistance. It's incredible how much our knowledge has changed in these 23 years. I first heard of prostaglandins in 1968 at one of the weekly sessions in Dallas from a visiting professor. Renal autoregulation was poorly understood and few incisive experimental studies had been done. The kinin system was just beginning to emerge and obviously no one had heard of atrial natriuretic peptide or endothelin.In this brief article, I'd like to review two facets of the renal circulation: autoregulation and various humoral agents which regulate renal vasomotor tone. Because of space constraints, this will be quite brief and I would refer interested readers to a more extensive review of the subject by Dr. Claudia Hura and myself [1].