Renal phosphate handling plays key role in phosphate metabolism. Kidney dysfunction induced hyperphosphatemia. The phosphatemia with renal insufficiency, especially uremia, indirectly progresses into secondary hyperparathyroidism via suppression of vitamin D/Ca system. This indirect effect on parathyroid is called "Trade-off theory". Recently, the direct effect of hyperphosphatemia on parathyroid has been reported independent of vitamin D/Ca system in renal failure. The control of serum phosphate is certainly important by restriction of phosphate intake in renal failure patients.