To date most of the work in organ transplantation has been confined to studies in dogs and human subjects.1,3,5,6 Investigation of transplantation immunity in such highly heterogeneous groups has been hampered, however, by lack of companion experiments in isologous recipients. Transplantation between inbred strains has many advantages, including more reproducible results, better controls, and a continuous supply of isologous tissue. Organ transplantation is difficult in the smaller mammals available as inbred lines, however, and with the exception of a series of kidney transplants in the rat,2 the study of transplantation immunity has depended heavily on use of skin or of transplantable tumors. Neither of these systems is ideal for investigation of early immunopathologic changes and their interrelations. The revascularization which occurs in both methods is further complicated in free skin-grafting by transient but intense epidermal cell activity, hyperplasia, and edema. An excellent discussion of these changes in isografts