By means of a number of balance studies utilizing different dietary intakes of Na and K, with concomitant measurement of urinary Na-retaining activity, the diagnosis of a left adrenocortical adenoma was made in a patient with hypertension, hypernatremia, hypokaliemia, alkalosis, and edema. This tumor and the left adrenal gland were removed, with subsequent disappearance of the aforementioned physical findings and electrolyte abnormalities. Assay showed higher concentrations of compound F, compound B, aldosterone, and desoxycorticosterone in the adrenocortical adenoma than in the left adrenal gland.