The aim of this work was to analyze patients suffering from primary hyperparathyroidism (HPT) treated by traditional and miniaccess surgery, to demonstrate the validity and limits of intraoperative assay of PTH (iPTH). Between January 2000 and December 2001, at the Surgical Science Department of "La Sapienza" University of Rome, 29 patients affected by HPT, one of whom was a recidivist, underwent surgery for HPT and had a mean follow-up of 15 months (range, 6-24 months). The research showed that a decrease of >50% in iPTH values is indicative of resolution of clinical signs in 95% of cases. The use of iPTH in HPT for solitary adenoma in both classical and mini-invasive surgery yields a 100% success rate in terms of persistence, recidivism, and postoperative normocalcemia. iPTH is of assistance to the surgeon and allows treatment through mini-invasive access. In the case of solitary adenoma, iPTH is not only a biochemical histological examination but also a predictive test of normocalcemia.