- Mice that possess mutations in the H-2 region were selected by means of skin grafting. We tested the survival time of thyroid grafts transplanted between C57BL/6 mice and their descendent H-2Kb mutant mice and compared the kinetics of skin versus thyroid graft rejection in each of the mouse strain combinations tested. The results demonstrated that reciprocal thyroid grafts between C57BL/6 mice and bm1, bm3, bm4, bm5, and bm6 mutants are accepted for long periods. The bm8 mutant appeared to be an exception because a small fraction of reciprocal thyroid grafts were rejected between bm8 and C57BL/6 mice. Transplantation of C57BL/6 mice with skin grafts from bm1, bm3, bm4, and bm8 donors induced rejection of subsequent thyroid grafts syngeneic with the skin. Thyroid grafts of bm5 and bm6 were not rejected by C57BL/6 mice even after preimmunization with bm5 and bm6 skin grafts. In contrast to skin grafts, innoculation of C57BL/6 mice with 50 X 10(6) spleen cells from mutant mice failed to immunize the recipients and induce rejection of mutant thyroid grafts. The results indicate that skin graft rejection assays and in vitro cell-mediated lympholysis (CML) typing can not always predict the consequence of transplantation of organs such as thyroid, and also that alterations in the H-2Kb molecule as a result of spontaneous mutations can give rise to mutated molecules that differ in their immunogenic and antigenic properties when expressed on thyroid cells, as compared with skin.