This publication comments on the recently published findings of a study by Eloot et al. (cJASN, 6: 1266–1273, 2011) that evaluated the correlation between several formulae for calculating estimated GFR (eGFR) and different low molecular weight uremic toxins; eGFRs were based on serum creatinine (SCrea), cystatin C (Cys C), or a combination of both. Unexpectedly, the correlations for the different solutes were highly inconsistent, irrespective of the eGFR formula. On the other hand, the different eGFR formulae gave consistent results per solute. Correlation coefficients for some solutes were low (hippuric acid, p-cresylsulfate, indole acetic acid, uric acid, asymmetric dimethylarginine) to nonsignificant (carboxy-methyl-propyl-furanpropionic acid). These data point to the fact that eGFR is a deceiving predictor of uremic solute concentration and their biological action; this inconsistency is very likely the result of the impact of other factors affecting concentration, such as tubular secretion, generation by intestinal flora and metabolism.