As it has been reported that opioids such as morphine and methionine-enkephalin induced antidiuresis and antinatriuresis along with decrease in renal hemodynamics when given intracerebroventricularly(ivt), the renal action of ivt naloxone, a pure antagonist of morphine, and its influence upon the morphine action were investigated in this study. Less than 0.3μM/kg naloxone ivt did not change renal funtion. 1μM/kg ivt tended to, increase urine flow rate and induce transient natriuresis. 3μM/kg ivt produced transient: natriuresis. 3μM/kg ivt produced marked diuresis and natriuresis without any changes of renal hemodynamics. 10μM/kg ivt produced significant increases of urine flow rate and excretion of sodium without any changes of renal hemodynamics. Morphine 0.03μM/kg ivt produced marked decrement in renal hemodynamics along with decreases of water and sodium excretion, as previously shown by Kang. These effects of ivt morphine were completely abolished by the pretreatment with 0.3μM/kg naloxone. These observations provide further evidence that opiate receptors and endorphins in the brain might play an important role in the center-mediated regulation of the renal function in the rabbit.