Recent data suggests possible net transport of urinary constituents across mammalian urinary tract epithelia (urothelia). To evaluate the effect of animal hydration status on such transport we instilled urine collected during two day water-deprivation, water-loading or ad-libitum water intake into isolated in-situ bladder(s) of groups of rats undergoing one of the same three hydration states. After 1 hour bladder dwell we retrieved the urine and measured differences in volume and solute concentration between instilled and retrieved urine. We previously reported results regarding changes in urine volume and net urea and creatinine transport and herein report the results of net urinary sodium, potassium, and chloride transport in the same animals. During water-loading conditions, urinary concentrations of Na, K, and Cl rose 4.9 mEq/L (30.7%), 2.6 mEq/L (16.5%), and 6.0 mEq/L (26.8%) respectively - indicating urothelial secretion into urine. During ad-libitum water intake urinary K and Cl concentrations fell 33.6 mEq/L (14.8%) and 28.4 mEq/L (12%) respectively (Na did not change) and during water deprivation urine Na, K and Cl concentrations fell dramatically by 53.2 mEq/L (18.6%), 159.4 mEq/L (34.6%) and 133.7 mEq/L (33.8%) - reflecting urothelial reabsorption of each ion. For each ionic species two factors independently influenced transport - the instilled urinary ion concentration, and the animal hydration state. These results demonstrate significant regulated ion transport across mammalian urothelia, support the notion that lower urinary tract modifies final urine, and suggest that the lower urinary tract may play a role in local and whole animal solute homeostasis.