This study was performed in order to certify the antidiuretic action and to investigate the mechanism of antidiuretic action of debrisoquin infused into a renal artery in dog. Debrisoquin, when infused into a renal artery, exhibited the antidiuretic action accompanied the reductions of glomerular filtration rate and renal plasma flow, and the decreased amounts of sodium and potassium excreted in urine, limited only to the infused side, while control kidney function remained unchanged at all. The antidiuretic action of debrisoquin infused into a renal artery was blocked by pretreament of prazosin, $alpha$$_1$-adrenergic blocking agent, or reserpine, catecholamine depleting agent. These results suggest that debrisoquin infused into a renal artery elicits antidiuretic action through indirect stimulation of renal sympathetic nerves.