Aminohydroxypropylidene diphosphonate (APD), a potent inhibitor of bone resorption, is used to control hypercalcemia in various diseases. It is less effective, however, in the management of hypercalcemia induced by primary hyperparathyroidism. We investigated the effect of APD on the bone metabolism of five patients with parathyroid adenoma. Before parathyroidectomy, 30 mg of APD was administered intravenously. Serum calcium decreased in all cases one to two days after APD administration, although it did not decrease to the normal range. Serum phosphorus also decreased. Urine calcium and hydroxyproline excretion, markers of osteoclasts activity, decreased dramatically. Serum alkaline phosphatase (ALP) and osteocalcin, markers of osteoblast activity, decreased after APD administration. Serum intact parathyroid hormone (PTH) and 1,25-dihydroxy-vitamin D (1,25[OH]2D) increased. These results indicate that APD is partially effective in the management of preoperative serum calcium level in patients with parathyroid adenoma. As osteoclasts activity is inhibited by APD, osteoblasts activity is also suppressed. Elevation of PTH and 1,25(OH)2D after APD-induced decrease in serum calcium level may explain the partial and limited effect of APD on lowering serum calcium in patients with parathyroid adenoma.