In an attempt to delineate the role of beta-adrenoceptors found to be existing in the brain tissue in the central regulation of renal function, isoproterenol, a β-adrenergic agonist, was administered directly into a lateral ventricle of the rabbit brain and the changes of renal function were observed. Also, the effects of propranolol, a specific β-adrenergic blocking agent, and its influence upon the isoproterenol action were studied. Isoproterenol, in doses ranging from 5 to 50μg/kg i.c.v., elicited antidiuresis which seemed to be related to the decreased renal hemodynamics brought about by the systemic hypotension. With moderate doaes of 15μg/kg the antidiuresis was less prominent and there was a tendency toward natriuresis, but with higher doses the natriuretic effect became less evident, overrun by the systemic hypotension. Propranolol, 500μg/kg i.c.v., produced little effect on the renal function, but it eliminated the antidiuretic action of 50μg/kg isoproterenol i.c.v. and reversed it to a diuretic and natriuretic one, along with increases in renal plasma flow and glomerular filtration rate. The systemic hypotension also was markedly attenuated by propranolol pretreatment. Thus, it was evident that the renal action of i.c.v. isoproterenol was not blocked by propranolol and became explicit only when the hypotensive action of isoproterenol which seems to he propranolol-sensitive is removed. Various possibilities to account for this disparity in sensitivity were discussed. It is suggested from these observations that the central β-adrenoceptors might also be involved in the regulation of renal function along with α-adrenoceptors, though less significant than the latter.