Reference values are reported for maximal renal concentrating capacity in children using intranasally administered desmopressin. The report is based on 591 tests in 473 healthy children aged 0.5-13 years. The concentrating capacity increased markedly during the first years of life and reached a plateau at the age of 3 years. The mean value minus two standard deviations was 525 mosmol/kg at 1 year of age and 825 mosmol/kg at 3 years of age.