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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.

1. The distribution of intravenously administered 18F was investigated in thirty-one normal human volunteers, seven patients with acute or chronic renal failure and two patients with malignant disease. The object was to define some features of the bodily distribution and handling of 18F in the hope that this will shed some light on fluoride physiology in health and disease. 2. Plasma radioactivity at any given time depends on the degree of diffusion of 18F through the extracellular fluid as well as on the competing effects of renal excretion and tissue uptake. The factors governing these last two functions are discussed. 3. At 1 h after injection 40% of the administered dose of 18F is contained in the extracellular fluid, 20% has been excreted and 40% taken up by the tissues, including 2·5% into erythrocytes.

Extra-renal excretion of diatrizoate has been demonstrated radiographically both in the rat and in patients with severe renal disease. Hepatic excretion in the bile is probably the chief source of the diatrizoate appearing in the stool which was found to be up to 20 per cent of the injected dose in 48 hours by radioisotope studies using 131I diatrizoate. The presence of an extra-renal excretory pathway may encourage radiologists to perform procedures involving the use of diatrizoate contrast media where these are likely to be of value in the presence of very severe renal failure and even anuria.