Proposed work continues to be aimed at elucidating the factors determining differences in rejection of different tissues, transplanted in different ways. Three endocrine tissues are being studied: thyroid, parathyroid, and pancreatic islets. These tissues are being transplanted across a variety of histocompatibility barriers and into several transplant sites, some possibly immunologically privileged. In the case of pancreatic islets, the vulnerability of isolated islets to rejection is to be compared with that of islets transplanted as part of the intact pancreas. Studies of the composite grafts of kidney and skin also continue. BIBLIOGRAPHIC REFERENCES: Ziegler, M.M., Reckard, C.R., Naji, A., and Barker, C.F. Extended Function of Isolated Pancreatic Islet Isografts and Allografts. Transplantation Proceedings 7:743-745, 1975. Perloff, L.J., Anderson, R.D., and Barker, C.F. Endothelial Repopulation of Venous Allografts. J. Surgical Research 18:131-136, 1975.