The preoperative localisation of parathyroid adenomas is difficult even for an experienced surgeon. The rate of unsuccessful exploration of the neck lies between 2 and 18%. This is mainly due to to anomalies and extremely small adenomas. In vivo staining with toulidine blue, isotopic labelled selenmethionin or angiographic localisation are uncertain procedures. More accurate results can be achieved through fractionized measurement of parathyroid hormone with selective venous catheterization. This method was applied in 47 out of 71 patients with a correct localisation being achieved in 77%. In connection with subtle laboratory diagnosis and repeated assessment of serum calcium and phosphorus, this procedure is the method of choice. In cases with normocalcaemia surgical indication should be considered with due reservation despite positive localisation.