Urodynamic pressure-flow studies (Whitaker test) of 28 kidneys (21 orthotopic and 7 transplanted) with equivocal obstruction of the upper urinary tract (UUT) yielded a sensitivity rate of 77.7% and a specificity rate of 75% in the orthotopic kidney, and sensitivity and specificity rates of 75% in the transplanted kidney. Trauma to the transplanted kidney (denervation, ischemia and surgery) does not modify the urodynamic of the pyelocaliceal system, thus conferring on the test the same diagnostic reliability as in the orthotopic kidney.