With a view to clarify the cause of so-called Banti's disease the author studied the adrenal cortical function in patients with this disease, and obtained the following results. 1. Elevation in the basal metabolic rates can be observed in many cases. 2. As for electrolytes in serum, sodium, potassium, chlorine and calcium are decreased, but phosphorus is increased to a high degree, while Na/K ratio is increased. 3. Robinsou Power-Kepler water test is positive in the majority of cases. 4. Blood sugar level in early morning is slightly high, and in the insulin sensitivity test, the insulin index has been found to have declined and restoration of lowered blood sugar is prolonged. 5. On measuring 17-KS and free chemocorticoids (Ch. C.) excreted in the urine, the amount of 17-KS is decreased conspicuously, but Ch. C. is increased slightly. 6. In the gel-ACTH loading test the adrenal cortical reserve function is declined. 7. After splenectomy the rate of the basal metabolism increases still further and the insulin sensitivity test yields about the normal values, but the adrenal cortical reserve function as observed by the gel-ACTH loading test does not show any change. 8. From these facts it is possible to assume that there is a decliue in the adrenal cortical function in this disease.