This studies were performed for investigation of mechanism on central antidiuretic action of L$_{G}$-Nitro-L-arginine (L-NOARG), nitic oxide systhase inhibitor, in dog. Antidiuretic action of L-NOARG infused into the carotid artery was not affected by renal denervation but inhibited by pretreatment with arginine, NO Precusor. Furthermore, L-NOARG inhibited the diuretic action of dopamine induced by hemodynamic development. Above results suggest that antidiuretic actions of L-NOARG mediated by endogenous substances not associated with renal nerve. Therefore, it is demonstrated that those endogenous substances might be associated with NO which mediate the diuretic action of dopamine.e.