This study was designed to assess whether reliability of quick intraoperative assay of intact (1-84) immunoreactive parathyroid hormone (iPTH) could allow us to quit after removing one (or several) enlarged parathyroid gland(s) and obtaining a normal iPTH level. Intact iPTH was assayed during surgery before removal of enlarged parathyroid gland(s) and 5, 10, and 20 minutes afterward. Forty-seven patients entered the study: 40 with primary hyperparathyroidism (32 with uniglandular disease and eight with multiglandular disease) and seven with secondary hyperparathyroidism; all underwent bilateral neck exploration. Among 32 patients with uniglandular disease, five had normal basal intraoperative levels, 25 demonstrated a clear-cut drop from supranormal to normal levels, and two had elevated levels. Among the eight patients with multiglandular disease, two had undetectable levels and two had normal levels after removal of the first enlarged gland. The seven patients with secondary hyperparathyroidism demonstrated a decline in PTH levels, suggesting hormone clearance similar to that of patients with primary hyperparathyroidism. In conclusion, quick intraoperative assay with intact (1-84) iPTH (1) is not hampered by renal insufficiency, (2) may overlook a second enlarged gland after removal of a first adenoma and obtaining normal iPTH levels, and (3) should not be used as a substitute for bilateral neck exploration.