Isoproterenol infusion (0.1 μ/kg per min) into the renal artery of the cat induced an increase in plasma renin concentration (PRC) from 14.3 ± 5.7 (mean ± SE) ng angiotensin I/ml per hr to 56.8 ± 7.7 after 70 minutes{P <0.05) and an increase in catecholamine secretion rate from 38.7 ± 6.0 ng/kg per 10 min to 180.0 ± 40.0 after 70 minutes(P< 0.001). Intravenous infusion of the same dose of isoproterenol had no significant effect on adrenomedullary catecholamine secretion rate. Isoproterenol induced preferential norepinephrine release: the ratio of norepinephrine to epinephrine secretion changed from 11.5:23.7 during the control period to 130.0:40.1 70 minutes after the start of isoproterenol administration. Intrarenal infusion of propranolol (3.0 mg/kg per min) inhibited renal renin release and adrenal catecholamine secretion in response to intrarenal isoproterenol. Intravenous infusion (0.4 Mg/kg P e r m in) °fan angiotensin II antagonist [Sar Ileu8]angiotensin II abolished the catecholamine response to intrarenal isoproterenol infusion. It is suggested that intrarenal isoproterenol infusion stimulates renal renin release and angiotensin production which, in turn, stimulates a preferential secretion of adrenomedullary norepinephrine.Circ Res 47: 835-839, 1980