The authors report observations concerning rejection and regeneration processes of allogenic peripheral neural tissue, depending on different genetic mismatches in a rat model. Five groups representing different rat strains (n = 100) were subjected to orthotopic grafting of 2.5-cm segments of sciatic nerve. Combinations represented different genetic barriers, including the Major Histocompatibility Complex (MHC), a non-MHC, a subgroup (A) of the MHC, a group representing MHC plus non-MHC, and an autologous control group. Animals were examined after one, two, and 12 weeks; additional evaluations in some of the experimental groups were done at six and eight weeks. Regeneration in varying degrees was evident in all groups at 12 weeks.