BACKGROUND The clinical usefulness of intraoperative parathyroid hormone (PTH) monitoring has been shown using an immunoradiometric assay (IRMA) with several significant limitations. PTH measurement by immunochemiluminometric assay (ICMA) is a nonradioisotopic technique that is more practical for use during parathyroidectomy. METHODS Plasma from a 15-second microcentrifugation was mixed with 2 antibodies, incubated at 45 degrees C, shaken at 400 rpm for 7 minutes, washed and counted for 2 seconds on a portable luminometer; PTH level was reported in 10 minutes. RESULTS Sixteen patients had multiple samples taken during parathyroidectomy. PTH levels measured 5 minutes after excision of a suspected abnormal gland were compared with preoperative or preexicision samples and either confirmed complete excision or indicated the need for more exploration in each patient. Correlation of 88 ICMA samples with standard 24-hour IRMA controls was excellent (r = 0.9218, P < 0.0001). The sensitivity of the test in predicting postoperative calcium levels was 94%. CONCLUSIONS This new assay can serve as a very practical adjunct for the parathyroid surgeon.