A prospective series of 200 patients with persistent hypercalcemia had an abbreviated diagnostic work-up consisting of parathormone radioimmunoassay, chest roentgenogram, intravenous pyelography, and serum protein electrophoresis. All patients with hypercalcemia and hyperparathormonism had neck exploration if roentgenograms failed to reveal evidence of ectopic hyperparathyroidism. Serum iPTH proved to be at least 96% accurate in predicting parathyroid disease while at the same time resulting in considerable diagnostic economy. An elevated iPTH was particularly helpful in distinguishing between hypercalcemia due to destruction of bone by malignancy and primary hyperparathyroidism with a coexisting malignancy. Further, measurement of parathormone was useful in evaluation of postoperative hypercalcemia.