Until now only a flap of the bladder or a loop of ileum have been used for either partial or total replacement of the ureters. Ureteric substitution by synthetic tubing would be an economical solution for ureteric replacement and would impose the smallest surgical risk upon the patient. Prior to the recent use of silicone rubber all the previous results with tantalum, latex and polyethylene have been disappointing. The first attempts using polyethylene, gave poor results (i0, Ii, 14, 15). Better results of short duration were reported using PTFE tubing (12, 18). Silicone prostheses were used by Blum et al. and Sankey (4, 5, 17). Auvert et al. have used a combined silicone textile graft since 1968 (i, 2, 9). In 1966, l<ohler (13) reviewed the literature concerning ureteric substitution by synthetic prostheses and concluded that plastic material was not suitable for permanent replacement of the urinary tract. The same opinion was given by Lhez in his report to the French Urological Association in 1968 (16). In our experiments, we have used a prosthesis of silicone rubber (polydimethyl siloxane), Scurasil R, (manufactured by Rhone-Poulenc). These artificial ureters are 15 to 25 cm in length and 5 to 9 mnm in external diameter. The inner surface is smooth and lacquered to prevent any calcification. To facilitate fixation, both ends are covered with a velvet sleeve of polyethylene glycol terephtalate (RhodergonR). The ends of the tube are inserted into the upper part of the ureter and the bladder. Sutures on the sleeve prevent migration of the tube. An anti-reflux valve is currently being tested. To prevent vesico-ureteric reflux we have incorporated a double leaf anti-reflux valve made with two thin silicone sheets. On the bench, this valve allows a direct i0 ml/min flow with a pressure drop of less than 1 cm of water. The back flow is lower than 1 ml/min with a reverse pressure of 40 cm of water. The leaflets should not reverse under a pressure of 80 cm of water. To prevent migration of the tube either distally into the bladder or proximally into the pelvis of the kidney a new prosthetic tube was designed with a spiral shape and this has proved to be more stable.