The aim of the present investigation was to study the functional characteristics and the long-term outcome after urinary diversion via a continent ileal reservoir. The villus height and absorptive capacity of ileal mucosa were studied in cats after exposure of the ileal mucosa to urine. In 16 patients at various intervals after their reservoir construction, the absorptive rate of L-phenylalanine was estimated after instillation of a test solution into the reservoir. The influence of the reservoir pressure was studied in 13 patients with empty and full reservoirs. The reservoir pressure was registered during renography and the volume recovered from the reservoir was measured. Twenty-one patients registered their emptying patterns and their emptying volumes during seven 24-hour periods. Urine samples were taken for determination of electrolytes (Na+, K+, Cl-), osmolality, pH and possible bacteriuria. Mucus in the urine was measured at various postoperative time intervals. Seventeen patients were followed postoperatively with a yearly determination of renal function and urography in special reference to the upper urinary tract. Routine blood tests, vitamin B12 in serum and base excess were also determined. In six patients, the excretion of titratable acid was determined after peroral loading with ammonium chloride. After exposing ileal mucosa to urine in cats, a significant decrease was found in the villus height and the absorption of water and electrolytes. This was true for the isotonic test solution but not for the hypertonic solution. The rate of active absorption of L-phenylalanine from the patient reservoirs decreased with the postoperative interval. With ordinary filling volumes, the pressure in the reservoir did not interfere with upper urinary tract drainage. The patients emptied their reservoir with a frequency similar to that of the voiding frequency of normal individuals. The 24 h volume was somewhat increased but the excretion of electrolytes and osmoles was normal. Bacteriuria was often present but, as long as reflux was prevented, it seemed to be of no harm. Mucus production did not diminish with time. Long-term follow-up (5-11 years) of renal function and upper urinary tract configuration disclosed that deterioration is infrequent and occurs only as a consequence of reflux or obstruction to flow. No metabolic disturbances have occurred.