Fibroblast growth factor (FGF) 23 was recently shown to alter serum phosphate level by modulating renal tubular phosphate reabsorption and production of active vitamin D independently of parathyroid hormone action. In addition, FGF23 was shown to be involved in the development of several diseases including autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR), X-linked hypophosphatemic rickets/osteomalacia (XLH) and tumor-induced rickets/osteomalacia (TIO). It has also been suggested that FGF23 physiologically regulates serum phosphate level because FGF23 null mice show high serum concentration of phosphate.