OBJECTIVE To study the effect of xenotransplantation with pig parathyroid cells, which was prepared using cell microencapsulation technique, on the treatment of hypoparathyroidism in rats without immunosuppressor. METHODS Parathyroid cells were isolated from 10 healthy newborn pigs and encapsulated in alginate-polylysine-alginate (APA) membranes. Thirty-two aparathyroid Wistar rats were randomly allocated to microcapsule, non-microcapsule, empty microcapsule, and control groups. Each rat was injected intraperitoneally with encapsulated porcine parathyroid cells, free porcine parathyroid cells, empty capsules or 0.9% NaCl, respectively. Total serum calcium and parathyroid hormone levels were monitored continuously for 40 weeks. And then, the transplant beds were retrieved and subjected to morphologic and electron microscopic examination. RESULTS In those animals xenotransplanted with microencapsulated porcine parathyroid cells, the calcium and PTH levels were consistently within the normal range during the 40 weeks. In contrast, no therapeutic effects were observed in rats in the non-microcapsule group. Furthermore, neither empty capsules nor 0.9% NaCl were shown to have any effect on the recipient's serum calcium or PTH levels. After 40 weeks, electron microscopic examination demonstrated that the parathyroid cells within the microcapsules had survived well in vivo. CONCLUSIONS Xenotransplantation of microencapsulated newborn pig parathyroid cells can successfully treat hypoparathyroidism in rats without using immunosuppressive drugs. The results of this study show the possible clinical use of microencapsulated porcine parathyroid cells.