We describe a modification to a commercially available immunoradiometric assay which reduces the turnaround time for parathyroid hormone (PTH) measurement to 1 h and permits intraoperative monitoring during parathyroidectomy. Alterations in PTH concentrations following removal of parathyroid tissue are compared with those of calcium, ionised calcium and phosphate. PTH measurements obtained intraoperatively permit definitive conclusions about the success of the operation within 1 h of sampling, allowing re-exploitation of the gland to take place immediately if necessary.