Pediatr Nephrol (2007) 22:514–520 1.038 1/L with a range of 0.06–4.89 1/L. In other studies involving 85 healthy adult subjects, the mean BRI values were similar, 0.89 ± 0.91 1/L. Higher BRI values have been described by Lewandowski et al. whose study group of 15 Caucasian adults demonstrated a mean BRI of 4.90 1/L, and 15 African adults had a mean BRI of 2.04 1/L [10]. The literature review did not reveal any larger or more comprehensive studies regarding BRI in children. Our findings in the large group of healthy children showed that the normal BRI value ranged from 0.06 1/L (5th percentile) to 1.93 1/L (95th percentile). The maximum values obtained in children were lower than those described by other authors in adult populations [6, 9, 20]. This may be due to the fact that the mechanism which inhibits crystal formation in children’s urine is more effective when compared to adults. Teller et al. observed that urinary glycosaminoglycans in children reduced the aggregation of crystals more effectively than in adults [21]. A similar age- related effect regarding stone formation has been observed by Bergsland et al., who showed that the urine of subjects aged less than 20 years produced a strong inhibitory effect on crystal formation [22]. Ricchiuti et al. investigated the process in boys aged less than 10 years and found increased activity of plasma protease inhibitor (inter-alpha inhibitor), blocking urinary crystallization during various stages [23]. Our results did not show a significant difference in BRI values between boys and girls. A minor difference was found in relation to age, but this was not significant. The BRI/1.73 m2 and BRI/kg behaved similarly. High correla- tions between BRI, BRI and body weight, and BRI and body surface area of studied subjects enable practical, more objective use of BRI and allow for comparisons between individuals. For this reason, these results are presented as median values with ranges for the 5th to 95th percentiles for the whole study group. The study has several limitations. So far, the use of our normative data appears to be limited to the Polish population. It is difficult to relate the results to other geographical regions or to different ethnic groups as there are no published data regarding BRI in children. Further comparative and prospective investigations are needed because a cross-sectional study is not able to reveal whether some children with a normal BRI value will be at risk for stone disease in the future. Moreover, some studied children may have had urolithiasis despite normal results of renal ultrasound. However, this study provided consistent nor- mative data on BRI, due to both the large age representation and the stringent selection criteria. 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