Between 1983 and 1992 thallium-technetium subtraction scintigraphy (TTS) was performed on 74 patients with clinical and biochemical evidence of hyperparathyroidism. Twenty-five of the 53 investigations since 1988 were conducted on patients with renal failure with a suspicion of secondary hyperparathyroidism. In a retrospective study we have evaluated radioisotope scintigraphy for patients with adenoma and for renal failure patients with possible parathyroid hyperplasia. Thirty of 74 patients underwent neck exploration. Scintigraphy detected 17 of 24 parathyroid adenomas (sensitivity 71%). In contrast, in six renal patients who came to operation, scintigraphy localised only 5 of 20 hyperplastic parathyroid glands (sensitivity 25%) and in one renal patient we localised a parathyroid adenoma. A review of the literature shows low detection rates for hyperplasia by TTS to be a common observation. Based on these findings a rational approach is offered for parathyroid localisation in renal patients prior to neck exploration.