Summary—The effects of irrigation with sterile and infected saline after acute ureteric dilatation by graded Teflon dilators were evaluated renographically and histologically in minipigs. The minipig ureter was dilated from its normal calibre of 4 F to 10 F, and 100 ml of sterile or infected saline were then introduced from a height of 60 cm under gravity.One week after irrigation and dilatation the ipsilateral kidney was either functioning less than 10% or there was an obstructive nephropathy. Histology at 3 months suggested that extravasation of infected irrigating fluid was the most likely cause of ureteric stricture formatio