Diagnostic ability of duplex Doppler ultrasonography reling on resistive index is limited when clinical symptoms and signs of rejection are subtle or renal dysfunction is caused by other conditions such as urinary tract infection. To investigate the significance in the changes of renal pelvis, a combined analysis of resistive index and ultrasonographic findings in cases of renal pelvis dilatation and mucosal thickening was undertaken. A mean resistive index was calculated from Doppler measurements of the main, segmental and interlobar arteries. The cause of mucosal thickening was retrospectively analysed using the clinical and laboratory findings. Twenty three cases of renal pelvis dilatation and 17 cases of mucosal thickening were found in a total of 159 renal transplantation cases. In 14 of the 23 cases with renal pelvis dilatation, renal function was normal and their mean resistive index was 0.64 $pm$ 0.04. Pelvis and ureter dilatation caused by ureteral stenosis or compressi n was demonstrated in 6 cases and their mean resistive index (0.72 $pm$ 0.05) was increased. Mucosal thickening of renal pelvis was found in 7 of 32 cases with acute rejection and in 2 of 13 cases with chronic rejection, but their mean resistive index was not different from that of the cases without pelvic mucosal changes. Three cases of acute rejection associated with urinary tract infection and 2 cases of chronic rejection in whom resistive indices were indeteminate, but mucosal thickening of the renal pelvis was prominet at ultrasonography. In renal transplant patients having indeterminate resistive index and mucosal thickening of the renal pelvis, ultrasonographic features must be correlated with the clinical and laboratory findings for an accurate diagnosis and treatment of renal dysfunction.