Secondary Hyperparathyroidism (SHPT) occurs in many patients with kidney disease and leads to bone disease. Active forms of vitamin D, calcitriol and paricalcitol, treat SHPT, but may have different effects on blood calcium. This study will randomize patients with SHPT and stage 3 or 4 CKD to treatment with calcitriol or paricalcitol, and monitor patients for the incidence of high blood calcium, and effectiveness of SHPT treatment.