 Patients who have been prescribed iron repletion therapy 100 mg IV every dialysis treatment for ten treatments by their primary nephrologist will be recruited for the study. Baseline blood samples will be obtained before and after each dialysis treatment for two dialysis treatments prior to the administration of iron. On the day of dialysis that iron therapy is started, blood samples will be obtained before and after the dialysis treatment via the patients vascular access. This procedure will be repeated each dialysis treatment for the ten sessions during which the patient is receiving intravenous iron. Subsequently, pre-dialysis blood samples will be obtained every week for four weeks after the administration of intravenous iron has been completed 