The site of a urinary tract infection (UTI) is located by clinical findings plus imaging techniques. Renal imaging with technetium 99mTc-dimercaptosuccinic acid (99mTc-DMSA) has shown promise but its efficacy for detecting acute pyelonephritis is still debated as is its ability to differentiate between acute, potentially curable disease and scarring, definitive changes.The files of all the 166 patients that underwent one or two (32 patients) 99mTc-DMSA imaging sessions for UTI in 1989 and 1990 in our department were analysed. The results of this technique were compared with the clinical and laboratory data and with those of other imaging techniques (ultrasonography and retrograde voiding cystourethrogram). The patients (92 girls and 74 boys, mean age: 5 years, range 15 days-17 years) were assigned to one of 3 categories: 1) acute pyelonephritis (27 patients), 2) low UTI (60 patients) and 3) uncertain UTI (79 patients), on the basis of the clinical and laboratory data.The first 99mTc-DMSA imaging was normal in 110 children; changes were unilateral in 45 and bilateral in 11 children. Images suggesting either acute or chronic changes were observed respectively in 19 and 48 children. 4 of the 7 acute changes were normalized on the second radioisotope scanning while 2 became worse; 19 of the 23 chronic changes were unchanged at the second scanning. Radioisotope scanning changes were seen in 81% of the patients classified as acute pyelonephritis and in only 27% of those with lower UTI. Reflux was detected in 56% of abnormal kidneys and in 36% of normal kidneys. The results of radioisotope scanning and ultrasound scan findings were not correlated in 24 patients (19 only abnormal radioisotope imaging, 5 only abnormal ultrasound scan).DMSA scans are useful for investigating and following UTI. They help to distinguish acute pyelonephritis and lower UTI. It is a reliable method of detecting structural abnormalities and identifying children at risk of progressive renal damage.