Both patient groups were also pair-matched for age and gender with 15 healthy adult subjects (control), who were usually the patient’s relatives or employees of the clinic. Only subjects who were in good health, were not taking medications, and had normal thyroid and renal function were included. It was possible to study prospectively six of the 15 patients with severe HPT who were submitted to parathyroidectomy 6 mo after the surgery. The study was approved by the Ethics and Research Committee of the Federal University of São Paulo, and informed consent was obtained from each subject.