The purpose of this study is to compare the pharmacokinetic 25(OH)D and 1,25(OH)2D responses to a single oral dose of vitamin D2 or vitamin D3 in a group of Stage 5-Chronic Kidney Disease subjects requiring chronic hemodialysis.

This is a randomized, single blind, controlled study. Subjects will be randomly assigned to receive 1) placebo capsules (control group); 2) capsules with ergocalciferol (the vitamin D2 group); or 3) capsules with cholecalciferol (the vitamin D3 group).

Inclusion Criteria:

• 30 men and women, ages 20-65, BMI 18-30, requiring chronic hemodialysis

Exclusion Criteria:

• They will habitually consume less than 16 oz of milk per day and get less than 10 hours of sun exposure per week. We will exclude those with granulomatous conditions, cirrhotic liver disease, and those taking anticonvulsants, barbiturates, or steroids in any form or any investigational drugs within 4 weeks. We will exclude those with pregnancy or planned pregnancy, hypercalcemia (>10.4 mg/dl) previously recorded, chronic GI disease which would interfere with absorption, any allergy to vitamin D3, or chronic vitamin D intake >1,000 IU daily. Subjects will continue to take a calcitriol analogue and phosphorus binder as prescribed by their nephrologist. Calcitriol analogues are to be documented and remain constant throughout study.