This study was performed in order to investigate the effect of renal function of NG-nitro-L-arginine (L-NOARG), inhibitor of nitric oxide (NO) synthase, in dog and ra bbit. L-NOARG, when given intravenously in dogs, exhibited the decrease in urine flow (vol), renal plasma flow (RPF), osmolar clearance ($C_{osm}$) and amounts of sodium and potassium excreted in urine($E_{Na},;E_K$). These renal functions of L-NOARG showed the same aspect in rabbit, too. L-NOARG, when administered into a renal artery, showed the same pattern as was obtained when given intravenously in both experimental and control kidney in dog. L-NOARG administered into the carotid artery showed the decrease in Vol, RPF, $E_{Na}$, in a low doses that did not show any effect when given intravenously. Above results suggest that L-NOARG produces antidiuretic action in dog and rabbit, and these antidiuretic actions may be mediated by central action.