1. The parathyroid hormone-like biological activity of concentrated urine was measured by the increase of plasma calcium concentration after intravenous injection of the sample into chickens.
2. Urine was tested in hypoparathyroid patients, normal volunteer subjects, primary hyperparathyroid patients before and after surgery and patients with secondary hyperparathyroidism.
3. In primary and secondary hyperparathyroidism the biological activity was significantly higher than in urine from normal subjects, which was in turn significantly higher than the activity in the urine of hypoparathyroid patients. This bioactivity diminished after surgical removal of a hyperparathyroid adenoma.
4. Decreased activity after trypsinization indicated the peptidic nature of the hypercalcaemic substance.