Transplantation of insulin-secreting tissues is currently being evaluated as a possible method of treating diabetic patients. Isolation of islets of Langerhans from the rat pancreas is now routinely accomplished, and methods for islet isolation from the human pancreas are being explored. Transplantation of isolated islets into isologous rats is capable of reversing streptozotocin-induced diabetes. Unfortunately, isolated islets are not immunologically privileged and various immunosuppression regimens have not effectively obviated the rejection phenomena seen in rat allograft experiments.