The goals of this study are to elucidate the function of extrarenal 1 alpha-hydroxylase activity in the setting of renal failure and to evaluate the role of nutritional vitamin D deficiency as a potential contributor to monocyte-associated inflammatory pathways in patients with end-stage renal disease (ESRD). This study will consist of patients on chronic maintenance hemodialysis three times per week who have been identified to have nutritional vitamin D deficiency. After consent for study enrollment, patients will undergo a 4 week washout period of all active vitamin D supplementation. After washout is complete, an blood sample will be obtained for baseline 25(OH)D levels and monocyte isolation for analysis by flow cytometry. Patients will then be started on cholecalciferol 50,000 IU twice weekly for 8 weeks. 25-vitamin D levels will be monitored midway through the treatment phase of the study and dosing adjusted as further described in detail within the protocol section. An additional blood sample will be drawn post-therapy for repeat 25(OH)D levels and monocyte isolation for flow cytometry analysis.