Hyperparathyroidism is no longer considered an uncommon endocrinopathy. Between 1994 and 2002, 138 patients underwent neck exploration for primary hyperparathyroidism at the Department for Surgery in the University Hospital of Dresden. Common reasons for operation failure are usually hyperplasia or remnant parathyroid tissue, inadequate parathyroidectomy at initial operation or the occurrence of abnormal hyperfunctioning supernumerary glands. To reduce the operation time, as well as the failure rate that accompanies the incomplete excision of hypersecreting parathyroid tissue, we perform an intraoperative monitoring of parathyroid hormone with an immunochemiluminometric assay (Nichols Advantagetrade mark Intact PTH). With modification of this assay, it was possible to perform the assay in the operating theatre and to attain the hormone values within 10 min. In all cases of successful operation with excision of the adenomatous parathyroid gland the PTH values declined to under 20 percent of the initial intraoperative PTH values. Our results declare the intraoperative parathyroid hormone monitoring as a cost-effective method to control the effect of surgical treatment.