Vitamin D analogues are in clinical use for prevention and treatment of secondary hyperparathyroidism (HPT) in chronic renal failure. Despite recent advances there is a need for vitamin D derivatives with maintained parathyroid hormone suppressive activity and less hypercalcemic and hyperphosphatemic toxicity. Here we show coincident increased expression of the vitamin D activating enzyme 25-hydroxyvitamin D(3) 1alpha-hydroxylase (1alpha-hydroxylase) and reduced expressions of the 1,25(OH)(2)D(3) catabolizing enzyme 25-hydroxyvitamin D(3) 1alpha-hydroxylase (1alpha-hydroxylase) in the majority of investigated parathyroid adenomas and secondary hyperplastic glands. In addition, this relationship was found for the mitochondrial CYP27A enzyme (25-hydroxylase), a potential physiological vitamin D(3) 25-hydroxylase. These findings should be considered in future development of vitamin D analogues for treatment of HPT.