BACKGROUND: Intraoperative parathyroid hormone (iPTH) assay (QPTH) in combination with preoperative localization, permits a less invasive operative approach in the treatment of hyperparathyroidism. A 50% reduction of the intraoperative PTH level, misured within 15 minutes with an immunochemestry system of III generation (ICMA), shows the completeness of the hypersecretive tissues surgical removal. PATIENTS AND METHODS: From June 2003 to December 2005 a series of 39 patients underwent target parathyroidectomy with intraoperative parathyroid hormone assay for parathyroid disease. Intraoperative PTH was measured before, 5-10 and 20 minutes after parathyroidectomy. 79.5% of patients had secondary hyperparathyroidism, 29.5% had primary disease. In 38 patients (97,4%) the intraoperative PTH levels declined more than 70% and in only one patient (2,6%) intraoperative PTH levels declined less than 50%. RESULTS AND CONCLUSIONS: QPTH has deeply modified the surgical approach to the treatment of hyperparathyroidism. Intraoperative measurement of iPTH is useful in prediction the complete removal of all parathyroid tissue after surgery for parathyroid disease, thus avoiding persistence or recurrence of disease and surgical failures. In well-studied cases QPTH can be considered a valid alternative to the intraoperative hystological examination.