1. The change in total body calcium content after surgery for primary hyperparathyroidism was studied in seven patients by whole body neutron activation analysis. Three patients who remained in the uncontrolled state for up to 12 months were also studied by this technique.
2. The technique and its reproducibility are described. Changes in total body calcium greater than ±4% should be detectable using this method.
3. The change in total body calcium after surgery was variable. Total body calcium content decreased in three cases after apparently successful parathyroidectomy. Not all the cases experiencing an increase in body calcium content had radiological evidence of bone disease.
4. The role of relative hypoparathyroidism due to suppression of normal parathyroid tissue by a functioning adenoma is discussed.