A 4.5-year-old boy was admitted to three different hospitals because of a tendency towards dehydration and polyuria, along with normal blood pressure, hypochloraemia, hypokalaemia, metabolic alkalosis and an impaired urinary concentrating ability. A renal biopsy failed to reveal juxtaglomerular hyperplasia. The clinical and laboratory findings failed to improve despite supplementation with potassium chloride and treatment with indomethacin. The urine was found to contain frusemide. The parents denied any drug administration to the boy. The child is now doing well more than 1 year after separation from his mother. Since ingestion of diuretic cannot be differentiated from true Bartter syndrome by blood and urinary electrolyte measurements alone, a diuretic screen is warranted in children with findings consistent with Bartter syndrome.