OBJECTIVE To evaluate the efficacy of rapid peroperative assay of parathormone in patients with primary hyperparathyroidism compared with the longer standard assay. METHODS Primary hyperthyroidism was diagnosed in 10 patients (8 males, 2 females, mean age 55 +/- 8.6 years, range 36-99) (preoperative tests: serum calcium 290 +/- 8.9 nmol/l, range 274-311; intact parathormone 137 +/- 31.3 pg/ml, range 87-250). First intention cervicotomy was performed. Blood samples were drawn at induction of anaesthesia, at palpation of the adenoma, and 15, 30 and 45 minutes after ablation. Each sample was assayed with a rapid radioimmunoassay and the longer standard laboratory methods. RESULTS There was a good correlation between the two assay methods. In the 9 patients with a solitary adenoma, serum levels of parathormone were normalized 15 (n = 8) or 30 minutes (n = 1) after resection. CONCLUSIONS Rapid radioimmunoassay is a reliable method for evaluating serum parathormone level peroperatively. Although financial implications may limit its use, this rapid assay is clearly indicated for patients in poor clinical condition undergoing first intention surgery and in those undergoing a second cervicotomy.