Because second generation PTH assays detect both 1-84 and 7-84 PTH fragments, the use of vitamin D analogues to treat secondary hyperparathyroidism could lead to excessive suppression of 1-84 and a preponderance of carboxy PTH fragments. As observed by Jono et.al accumulation of 7-84 could contribute to excessive vascular calcification. We hypothesize that limiting the accumulation of 7-84 PTH fragments by maintaining a 1-84/7-84 ratio above 1.6 will reduce the amount of vitamin D analogues administered and ultimately reduce the development of coronary calcification. To investigate this hypothesis, we propose to prospectively treat 50 patients with 1, 25 dihydroxyvitamin D2 where doses are determined by maintaining a 1-84/7-84 ration > 1.6 or by maintaining intact PTH levels between 150-350 pg/ml using existing second generation PTH assays.