To investigate the putative role of FGF23 as a mediator of renal fibrosis, we sought evidence of ectopic renal production of FGF23 in response to unilateral ureteric obstruction (UUO), and determined the effects of FGF23 on renal interstitial fibroblast activation and function in vitro. This evidence concerns the gene FGF23 and renal fibrosis.