The pelvic pressure was measured with a noninvasive technique in 7 pigs with a total unilateral obstruction of the ureter lasting 4 weeks. Pressure measurements were performed once a week. Although there was a wide pressure variation both intra- and interindividually during the 4 weeks, all systems had an elevated pressure (greater than 25 cm H2O) after 4 weeks. This study shows that the pelvic pressure can remain elevated in the chronically totally obstructed pyeloureter.