An experimental model of colonic urinary diversion was performed on male Wistar rats to see if faeces, urine or a faeces and urine mixture produces tumours. Cell kinetic techniques, including the crypt cell production rate, and cellular DNA measurement were used to examine the effect of urine and of faeces on the colonic mucosa. Urinary diversion into the colon significantly increased colonic crypt activity. Tumours were found at the anastomosis when urine and faeces were mixed at 4 months, and at 6 months with urine alone.