Peroperative assay of intact parathormone has been proposed to improve the surgical results, either by confirming cure peroperatively or to indicate the need for further search in case of persistent pathological secretion. Between October 1992 and July 1994 parathormone was assay peroperatively during 136 operations for primary hyperparathyroidism in 135 patients. Seven samples were made for each patient in the operating theatre: at intubation, at skin incision (ti), at ablation of the pathological gland, then 15 (t15), 30 (t30) and 60 (t60) minutes later. All samples were assayed with the rapid technique and controlled the next day with the standard method. The correlation coefficient between the two methods was 0.97. Comparing the drop in intact parathormone levels between cured patients and those with persistent hyperparathyroidism after surgery showed statistically significant differences. We retained a dramatic drop in hormone level by 80% between t1 and t15 with persistent low levels between t15 and t30 (ratio t30 over t15 < 1) as the criteria of cure: the drop off between t1 and t15 is not sufficient to confirm cure. Peroperative assay of intact parathormone can be used to demonstrate the presence of remaining pathological parathyroid tissue, especially important in case of highly ectopic localizations. This assay technique is not particularly well adapted to routine parathyroid surgery for primary hyperthyroidism but has been reserved for cases planned for limited dissection (operations conducted under local anaesthesia and reoperations).