Hypokalemia in Bartter's syndrome (BS) is often difficult to correct despite all measures. Amiloride is a new potassium-sparing diuretic that blocks sodium channels in distal renal tubular cells, independent of aldosterone. Four patients with BS were studied, in an outpatient clinic, while on amiloride therapy (10 to 40 mg/day). Before receiving amiloride the patients were treated with combinations of prostaglandin synthetase inhibitors, potassium-sparing diuretics, and potassium supplements. After a baseline observation period, the potassium-sparing diuretics were discontinued and amiloride therapy was instituted. Cumulative mean plasma potassium level rose after amiloride (0.5 mEq/l; P less than 0.05). The mean plasma potassium levels in three of the patients rose and one of these patients eventually became normokalemic. There were very few adverse reactions and none could be attributed to amiloride alone. Amiloride may be a useful and safe drug for the treatment of the hypokalemia of BS.