Metabolic clearance rate and half-time of arginine vasopressin were measured in 43 cirrhotic patients and 10 control subjects. Synthetic arginine vasopressin was infused intravenously at a rate of 500 pg/min/kg of body weight for 75 min. The metabolic clearance rate was significantly reduced, and the half-time of arginine vasopressin after stopping the infusion was significantly increased in patients with cirrhosis, particularly in those with ascites and in those with moderate or severe liver dysfunction. Changes in metabolic clearance rate and half-time of arginine vasopressin correlated with the score of the liver dysfunction, prothrombin activity and levels of serum albumin and bilirubin but not with parameters of kidney function (serum creatinine levels and clearance of creatinine). We conclude that reduced metabolic clearance rate and prolonged half-time of vasopressin in plasma are frequent findings in cirrhotic patients with poor liver function. This impaired catabolism of antidiuretic hormone may contribute to maintaining elevated plasma levels of this hormone in these patients and may be an additional factor leading to fluid retention and to dilutional hyponatremia. (HEPATOLOGY 1992;16:974–979.)