Intraoperative measurement of intact parathyroid hormone (PTH) can be used to evaluate the success of parathyroid surgery in primary hyperparathyroidism associated with parathyroid adenoma. To evaluate this approach we used a modified immunoradiometric assay (IRMA) to study the kinetic patterns of circulating PTH disappearance in 13 patients undergoing adenomectomy for single adenoma. The rapid and the standard assay for PTH measurement in plasma were used and compared. The two methods showed a highly significant correlation (r = 0.995; p < 0.0001). We reported a decrease in PTH to 18.2 +/- 2.30 (mean +/- SEM) from baseline values at 15 minutes after successful parathyroid adenomectomy in the 13 patients. The biphasic pattern of serum PTH clearance was calculated in 8 of the studied patients with a fast phase showing a half-life (T1/2) of 3.99 (SEM 0.464) minutes and a slow phase with a T1/2 of 91.0 (SEM 33.6) minutes. Half the amount of the basal values was reached between 4 and 9 minutes. Our study concludes that the modified IRMA for intraoperative measurement is feasible, reliable and sufficiently precise for low hormone values. Since it may yield information on the half-life of PTH in the circulation, it may play a role in the surgical guidance for total exeresis of hyperfunctioning tissue.