The plasma concentrations of low molecular weight proteins such as retinol binding protein (RBP) and β2-microglobulin (β2M) reflect the glomerular filtration rate (GFR) Plasma low molecular weight protein concentrations may provide more accurate estimates of GFR in utero than plasma creatinine concentration (PCr). The aim of this preliminary study was to develop a method for measurement of plasma RBP concentration by ELISA, establish a normal range in children and the correlation with GFR in children with renal disease, and to compare it with PCr and plasma β2M as predictors of GFR estimated from the plasma clearance of 51Cr-EDTA by single exponential analysis 123 children aged 6.2±4.3 years with nephrological and haematological diseases were investigated. Their PCr ranged from 13 to 471μmol/L and GFR from 6 to 283ml/min/1.73m2. There were significant positive correlations between RBP and PCr (r=0.78), β2M and PCr (r=0.82), and RBP and β2M (r=0.75). Significant negative correlations were found between GFR and PCr (r=0.61, p<0.001), β2M (r=0.63, p<0.001) and RBP (r=0.53, p<0.01). Conclusion: Plasma RBP reflects GFR, but provides a less precise estimate than plasma β2M. It is not clear which, if either, would better reflect GFR in utero.