The viability of syngeneic, allogeneic and xenogeneic bone grafts was investigated in mice and rats by the polymerase chain reaction method using carcinoembryonic antigen transgenic mice as donors. DNA of syngeneic grafts was detected more than 24 weeks after bone grafting. In contrast, the DNA of allogeneic thymic grafts and xenogeneic bone grafts disappeared by 3 weeks after transplantation. However, DNA of allogeneic bone grafts was detected until 20 weeks after transplantation. Histological examination at 12 weeks after surgery detected some donor nuclei in both syngeneic and allogeneic bone grafts.