1. The decrease of antidiuretic potency in the blood was studied in anaesthetized rats after the intravenous injection of vasopressin (100 mU/100 g) and was shown to follow an exponential course. 2. Removal of the kidneys retarded the rate of disappearance of injected vasopressin from the circulation, and so did tying of the coeliac and mesenteric arteries. 3. In rats in which the kidneys had been removed and the coeliac and mesenteric arteries had been tied, the disappearance of vasopressin was almost entirely prevented. 4. It was concluded that under the experimental conditions used, the extraction of vasopressin was almost complete after the passage of blood through the kidneys and the splanchnic vascular bed. 5. The kidneys accounted for about 50 % of the vasopressin cleared, and the splanchnic vascular area for at least 40 %. 6. The antidiuretic activity found in the urine after the intravenous injection of vasopressin into unanaesthetized rats was equivalent to 6·7 % of the dose administered.