 After a one month run-in phase, the patients received sequentially a low dose 6.25 mgday, an intermediate dose 12.5 mgday, and a high dose 25 mgday of hydrochlorothiazide HCTZ, each dose being administered for a period of two months. Amiloride 5 mgday was started at the beginning of the study, and continued throughout the sequential trial to reduce the risk of HCTZ-induced hypokalaemia. For safety reasons, two patients did not receive the last 25 mg dose of HCTZ because of a body weight BW 25 kg. The last HCTZ dose was followed by a one month withdrawal period phase E. 