Morphine has been known to produce antidiuresis when given directly into a lateral ventricle of the rabbit brain, mainly through hemodynamic changes brought about by nerve stimulation to the kidney. This study was attempted to find out whether adrenergic fibers are involved in the action. Phentolamine, a potent alpha-adrenergic blocking agent, induced antidiuresis when given intravenously in a dose of 2 mg/kg. Morphine administered intracerebroventricularly 40 to 60 min. after phentolamine, when its effect is at the maximum, produced antidiuresis and typical changes in renal function, uninfluenced by the phentolamine pretreatment. This observation indicates that adrenergic fibers do not participate in the renal action of intracerebroventricular morphine and it is suggested that nerve fibers of other types might be involved in the action.