We present the results obtained in the follow-up of 66 children with vesico-ureteric reflux (VUR) of different grades (111 refluxing renal units, RU; the VUR being bilateral in 47 children), employing the renal cortical agent 99mTc-aprotinin (TcA). Together with the visual inspection of the scan, we adopted a quantitative approach, expressing the results as the split percent uptake of the injected dose. The detection of morphological anomalies was more frequent in the cases of more severe reflux. Scars were noted in 38 RU, with a higher prevalence in more severe grades, except for grade V where severe impairment was more frequent. With regard to the amount of functioning parenchyma, the probability of a significant loss of nephrons (expressed by a low uptake of TcA), rose with the grades, although the higher grades were not invariably associated with parenchymal failure. The abnormality detection rate is higher by about 2:1 with the TcA scan than with other diagnostic modalities such as i.v. pyelography or echography. No differences were found between RU with or without scars as regards evolution over time; only when the TcA uptake at presentation was lower than 10% was the normal development of the RU likely to be hindered. From these data it can be concluded that early diagnosis is the key factor in the management of these children with VUR; the morpho-functional assessment with TcA uptake is probably the most effective technique for the detection of parenchymal abnormalities. In addition, the test has a high prognostic value, an uptake lower than 10% indicating an unfavourable prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)