A recently developed chemiluminescent immunoassay for 1-84 intact parathyroid hormone (PTH) demonstrated increased specificity by virtue of two-site antibody binding and increased sensitivity by use of a chemiluminescent technique. Basal PTH levels were measured in three groups of subjects: (1) normal (n = 82), (2) hyperparathyroidism (n = 31), and (3) patients with hypercalcemia of malignancy (n = 16). There was good discrimination between normal (1.2 to 9.4 pmol/L) and hyperparathyroid subjects (9.2 to 53.4 pmol/L). In persons with hypercalcemia of malignancy all PTH levels were within the normal range (0.8 to 5.2 pmol/L) or suppressed. PTH release was stimulated by the intramuscular injection of 100 IU salmon calcitonin in 6 normal controls, 10 patients with primary hyperparathyroidism due to adenoma, and 5 with four-gland hyperplasia. There was no significant rise in PTH concentration and out of the normal range in the control subjects, but the adenoma patients demonstrated a mean rise of 24.4%, 26%, and 33%, and hyperplasia patients, a mean rise of 37%, 47%, and 37% over basal levels at 120, 180, and 240 minutes. The mean absolute rise in PTH concentration was 13.4 +/- 7.7 pmol/gm of parathyroid tissue in the adenomas and 27.2 +/- 9.5 pmol/gm of parathyroid tissue in the hyperplastic glands; this difference was significant (p less than 0.05). Serial blood samples from a central vein were taken at surgery for hyperparathyroidism, and the rate of decay of the intact hormone was studied in 9 patients after removal of the parathyroid tissue. This decay was rapid with a half-life of 300 seconds. We conclude that this new specific and sensitive intact PTH assay will provide a valuable means of investigating dynamic aspects of parathyroid physiology.