In experiments on rats we studied reabsorption and secretory activity of the mucosa in isolated segments of the ileum and sigmoid colon used for urinary bladder intestinoplasty after cystectomy. Ileal mucosa was found to retain high metabolic activity under changed conditions. It reabsorbs urea, creatinine, potassium, sodium, chlorine, phosphorus, calcium, glucose, and uric acid from the urine and secretes magnesium, iron, and proteins into the urine. Sigmoid mucosa appeared to be less active in terms of reabsorption of the studied urine metabolites, but more actively secreted calcium and magnesium into urine and additionally secreted sodium. It was accompanied by an increase in blood concentrations of urea, creatinine, glucose, phosphorus, magnesium (only for sigmoid colon) and development of hypoproteinemia. These findings are important for investigation and prevention of metabolic complications after urinary bladder intestinoplasty.