Liddle's syndrome was diagnosed in a 23-yr-old Chinese girl with hypertension and hypokalemia by the presence of suppressed renin and negligible plasma and urinary aldosterone secretion. Adrenal corticosteroids, including aldosterone, were suppressed by dexamethasone and stimulated by ACTH. While spironolactone was ineffective, triamterene (2,4,7-triamino-6-phenyl-pteridine) treatment corrected the hypertension and hypokalemia and restored PRA to normal provided that sodium intake was not excessive. During long term treatment with triamterene, blood pressure was extremely sensitive to salt intake, increasing promptly with high intake and decreasing with low salt intake. As a result of the chronic hypervolemia and sodium retention consequent upon the patient's persistent high salt intake and increased renal tubular sodium reabsorption, plasma renin and aldosterone remained low. Erythrocyte sodium concentration and membrane permeability were increased. Triamterene with salt restriction was able to lower the intracellular sodium concentration but did not correct the increased sodium permeability. This suggests that there is an abnormality of sodium transport in Liddle's syndrome which affects the erythrocytes as well as the renal tubular cells.