The effect of Kappa-agonist dynorphin A-(1-13) on the urine flow was studied in ethanol-anesthetized rats. Intracerebroventricular injection of dynorphin A- (1-13) (5 micrograms, 10 micrograms) induced a potent diuretic response with insignificant action on mean arterial pressure and heart rate. The diuretic response began to show at about 20 min after injection and lasted 120 min. This diuretic effect could be almost completely blocked by pretreatment with naloxone (20 micrograms) or atropine (10 micrograms).