1. Aldosterone-producing adenomas were located before operation in eighteen patients by comparison of aldosterone concentrations in blood obtained by percutaneous catheterization of the adrenal vein or renal vein. The concentration of aldosterone in the venous effluent from the adrenal glands containing adenomas was significantly greater than in the venous effluent from contralateral glands.
2. Catheterization of the adrenal vein is, however, technically difficult. The location of adrenal adenomas was also possible by analysis of blood from the renal vein.
3. If the concentrations of aldosterone in blood from the left renal vein were higher than those from the right, the existence of a left adrenal adenoma was suggested. A high value in plasma, obtained from the inferior vena cava above the entry of the right adrenal vein, showed a right adrenal adenoma. This procedure identified very small functional adenomas which could not be demonstrated radio-graphically, or seen or palpated at surgery.
4. It was concluded that differential aldosterone measurement after percutaneous bilateral adrenal vein or renal vein catheterization can be used as a definitive test for the location of an aldosterone-producing adenoma, where this is uncertain.