Given the importance of phosphate in several biological processes, in the present study we investigated the effects of 1) increased dietary phosphorus intake and 2) phosphorus deficiency on erythropoiesis and iron metabolism in association with FGF23, using either dietary intervention in the form of high (1.2% Pi and 1.65% Pi) or low phosphorus (0.02% Pi) diet in mice with normal kidney function, or a mouse model of X-linked hypophosphatemia (XLH), the most common genetic disorder of phosphate homeostasis. The gene discussed is FGF23; the disease is X-linked hypophosphatemia.