Eleven ureteral replacements by Rhodergon-Scurasil® protheses were performed in 7 dogs. The production of the prothesis and the technique of the operation are described. Slight dilation of the upper urinary tract, noted 10 days after operation by X-ray television and IVP, diminished continuously thereafter in all dogs. Bilateral substitution of the ureter was done in 4 dogs. Following the replacement of the second ureter by a prothesis, the side first operated upon again showed a moderate dilation, while the second side remained highly satisfactory. Evacuation of the urine via the rigid prothesis was assured by peristaltic waves initiated in the remaining 2 cm of the upper ureter. In order to avoid vesicoureteral reflux in future experiments, a model of a sleeve-valve mechanism is presented