To verify the role of mAbCD28 in allograft transplantation. The biological action of mAbCD28 had been tested in mixed-lymphocyte-reaction and parathyroid gland allotranplantation in rats. Results: mAbCD28 could significantly suppress the proliferation of T cells in vitro and prolong the survival time of allograft in vivo. The results showed that mAbCD28 could block the costimulatory signals transmitted by CD28 molecules, and played an immunosuppressive role in parathyroid gland transplantation in rats.