Paricalcitol (Zemplar) is a synthetic vitamin D(2) analogue that inhibits the secretion of parathyroid hormone (PTH) through binding to the vitamin D receptor. It is approved in the US and in most European nations for intravenous use in the prevention and treatment of secondary hyperparathyroidism associated with chronic renal failure in adult, and in the US paediatric, patients. Paricalcitol effectively reduced elevated serum PTH levels and was generally well tolerated in children and adults with secondary hyperparathyroidism associated with chronic renal failure. In well designed clinical trials, paricalcitol was as effective as calcitriol and as well tolerated in terms of the incidence of prolonged hypercalcaemia and/or elevated calcium-phosphorus product (Ca x P). Preclinical and in vitro studies have demonstrated that paricalcitol's biological actions are mediated through binding of the vitamin D receptor, which results in the selective activation of vitamin D responsive pathways. Vitamin D and paricalcitol have been shown to reduce parathyroid hormone levels by inhibiting PTH synthesis and secretion.