Protein-bound uremic toxins (PBUTs) accumulate in chronic kidney disease (CKD) and are poorly removed by dialysis. Gryp et al. demonstrated that fecal bacteria from patients with CKD do not produce more PBUTs than do those from healthy controls and that the accumulation of PBUTs, as CKD progresses, is mainly due to their reduced renal elimination by glomerular filtration and tubular secretion. This work underlines the importance of studying the metabolism of PBUTs along the diet-gut-liver-kidney axis. Copyright (C) 2020, International Society of Nephrology.