An important way of examining adrenocortical function is the analysis of adrenal venous blood. In the rat, owing to the small dimensions, direct cannulation of the adrenal vein is not suitable for routine work. Vogt (1954) overcame this obstacle by collecting adrenal venous blood from the left renal vein. However, ligation of the renal pedicle disturbs physiological conditions, and if the kidney plays any role in aldosterone regulation, Vogt's method cannot be considered suitable for experiments on aldosterone secretion. In order to avoid the disturbance of the renal circulation during the collection of adrenal venous blood, the following method has been developed. After ligation of the renal end of the left adrenal vein, the vessel is opened carefully (but not transsected!). Adrenal venous blood flows without resistance through the aperture into the abdominal cavity. In order to prevent intravascular clotting the animal is heparinized. A reduction in the rate of