Renin release from renal cortical slices of baboon kidneys was measured. The basal release rate was directly proportional to the renin content. Release was stimulated in a dose-dependent fashion by isoproterenol and was inhibited both by angiotensin II and vasopressin. Maximum inhibition was approximately 30%. Experiments also were done in which angiotensin II and converting enzyme inhibitor were infused into the lateral ventrical of anesthetized baboons. Angiotensin caused a reduction in plasma renin activity (PRA), and converting enzyme inhibitor an increase in PRA, independent of changes in blood pressure.