We report on two siblings suffering from a new congenital tubulopathy. Following normal pregnancies not complicated by polyhydramnios, severe renal losses of potassium, chloride, sodium and magnesium occurred in the first weeks after birth. Calcium metabolism was not affected. The distal tubular chloride reabsorption was considerably decreased in the two siblings (0.25 and 0.28, respectively). Secondary hyperaldosteronism, activation of the kallikrein-kinin system and elevated urinary prostaglandin excretion were observed. The effects of indomethacin, spironolactone and captopril on symptoms, electrolyte wasting, activation of renin-angiotensin-aldosterone and kallikrein-kinin system and prostaglandin synthesis were studied. In spite of persisting elevation of prostaglandin synthesis, captopril decreased electrolyte wasting, polyuria and hyperaldosteronism most effectively. CONCLUSIONS We delineate an apparently new disorder characterized by a postnatal onset, an extremely decreased chloride reabsorption with extensive hyperchloriduria and hypermagnesiuria in the presence of normal calcium metabolism. The disorder can be distinguished from other tubulopathies with hypokalaemic alkalosis.