Ureric function in five women undergoing Wertheim hysterectomy for carcinoma of the uterine cervix was assessed from intra-ureteric pressure recordings made with a new technique. No notable difference was found in frequency, rate or amplitude between the uretero-peristaltic waves recorded immediately before and after dissection of the ureter. In three cases, however, retro-peristalsis occurred and in two of them it persisted throughout the operation. The presence of retrograde peristalsis may indicate that the peristaltic activity of these ureters was disturbed by the operative manipulation. Ureteric stasis was also demonstrable by radiographic techniques in those cases in which retro-peristalsis occurred during the operation but not in those in which it was absent.