Patients with end stage renal disease often have secondary hyperparathyroidism due to high phosphorus and low calcium levels in the blood. Preliminary animal studies and our initial human study indicate that the parathyroid hormone levels may change quickly based on the ingestion of phosphorus, prior to any change in the blood levels of calcium or phosphorus. This follow-up study will attempt to determine if the effect is independent of an increase in the blood glucose level. If so, this would suggest an as yet unidentified gastrointestinal receptor that mediates parathyroid hormone levels. This may affect the timing of administration and the type of phosphate binder used in treating patients with secondary hyperparathyroidism. The knowledge that parathyroid hormone levels can change acutely may also affect the recommended timing of blood samples