Preoperative electrolyte concentrations in parotid and submaxillary saliva were compared retrospectively from patients with true and pseudoprimary aldosteronism as well as patients with essential hypertension and normal subjects. Patients with primary aldosteronism due to an adrenal adenoma uniformly exhibited an increased potassium concentration in their submaxillary gland secretion. The range of values exhibited by these patients did not overlap with the consistently normal values observed in patients with essential hypertension and also in patients with pseudoprimary aldosteronism (associated with adrenal hyperplasia). This measurement may, therefore, be useful in identifying patients with primary aldosteronism and in separating them preoperatively from the clinically similar entity of pseudoprimary aldosteronism.