VARIOUS elements have been considered as causing edema or ascites in patients with hepatic cirrhosis, and especially has antidiuretic substance been considered to be a factor in the production of ascites in liver disease. Since Malaguzzi-Valeri et at. pointed this out in 1941 (1), studies have been made by many others, among them Ralli et al. (2), Lloyd and Lobotsky (3), Perry and Fyles (4) and Goldman and Luchsinger (5). The ayes and nays are about equally divided, and there is still no true identification. In this paper is presented a study which the authors recently undertook in an effort to clarify the decreased inactivation of antidiuretic substance in the liver of patients suffering from portal hypertension. Liver fragments were removed for in vitro study, and then antidiuretic substance was injected into the portal vein. Various biologic methods have been used for this purpose; we selected that of Jeffers and associates (6) which is said to be most sensitive. Male adult rats were used each weighing 150–200 Gm., all bred in the same circumstances with a diet of solid food and unlimited water. A volume of 12 per cent ethanol-water solution equivalent to 5 per cent of the body weight and previously warmed to body temperature is forced into the stomach. After thirty minutes (with the rat in a narcotized condition) a volume of warm water equivalent to 3 per cent of the body weight is introduced in the following way: The rat is fixed on a board on its back. By vesicotomy, a fine vinyl tube is inserted into an incision made in the urinary bladder, and the urethra is bound. For the first twenty minutes, the volume of urine is measured every five minutes as it drops through the vinyl tube. When the excretion is the same for each five-minute period, 0.2 ml. of the material to be tested is injected into the femoral vein. For the second twenty-minute period, the volume of urine is measured every five minutes and the total volume compared with the total volume during the first twenty-minute period before injection. Thus the ratio between the two periods is found.