The effect of saline and/or water load on diuresis, natriuresis and kaliuresis in control and in neonatal or adult capsaicin-pretreated awake rats has been assessed. Urine was collected by means of metabolic cages or intra-abdominally from a previously catheterized ureter. Neonatal but not adult capsaicin-pretreated animals exhibited a remarkable reduction in volume of urine output and in electrolytes excretion. This effect was more evident following saline as compared to water load. Similar results were also obtained when urine was directly collected from the ureters, suggesting that pharmacological ablation, at neonatal stage, of a subset of capsaicin-sensitive sensory nerves could impair the excretory kidney function.