It has been suggested that determination of differential renal function (DRF)using technetium-99m dimercaptosuccinic acid (DMSA) may lead to overestimation of the function of an obstructed kidney in patients with excretion abnormalities owing to pelvic retention of DMSA. Recently published guidelines have recommended use of furosemide injection when calculating DRF in these particular patients. The aim of this study was to evaluate the effect of diuretic administration on the determination of DRF using DMSA scintigraphy. For this purpose, 19 patients, aged from 1 month to 69 years (19.4+/-24.8 years, 15 males, 4 females), in whom pelvic retention had been documented by diuresis scintigraphy were included in the study. DMSA scintigraphy was performed in all patients 2-4 h after injection and six planar images were obtained. Immediately after the standard study, furosemide was injected in all patients, and 30 min later the same number of images was obtained. DRF was calculated for each patient and from each DMSA study by using the arithmetic mean method. The difference between two studies (DMSA scintigraphy with or without furosemide administration and diuresis scintigraphy) was expressed as a percentage of the mean value of the two studies (the DRF value of the affected kidney was thus taken into account). The mean of the differences represented the systemic bias and the SD of the mean of the differences represented the precision of the technique. In seven patients, diuresis renography revealed an obstructive curve pattern. We did not observe any significant difference between the DRF values obtained before and after diuretic administration (P>0.5). When we compared DRF values obtained from standard and from diuretic DMSA studies, the mean of the differences was only 0.3% and the SD was only 1.2%. There was also no significant difference in DRF between patients with the obstructive curve pattern and those with a dilated renogram curve pattern (with washout of activity during the second phase of the study) (P>0.1). In conclusion, we did not observe interference from pelvicalyceal activity in patients with documented pelvic retention and infer that diuretic administration may be a useless intervention for improving the accuracy of determination of DRF.