This study was performed in order to investigate the effect of ketanserin, a specific antagonist of 5-HT2 receptor, on renal function in dogs. Ketanserin (50.0 and $150.0{;}mu extrm{g}/kg$), when given intravenously, produced antidiuretic action accompanied with the decreased amounts of sodium and potassium excreted in urine (ENa, EK) and the increased reabsorption rates of sodium and potassium in renal tubules (RNa, RK). Ketanserin (50.0 and $50.0{;}mu extrm{g}/kg$), when administered into a renal artery, elicited antidiuretic action in both experimental and control kidney, this time changes of renal function showed the same aspect as when given intravenously. Ketanserin (15.0 and $50.0{;}mu extrm{g}/kg$) injected into the carotid artery exhibited also antidiuretic action and this antidiuretic action was not affected by renal denervation. Above results suggest that ketanserin elicits antidiuretic through central function, this central antidiuretic action is not mediated by renal nerves.