Experimental islet transplantations in pancreatectomized and streptozotocin-treated diabetic allogeneic and partially inbred rats are considered with respect to transplantation site and immunological factors responsible for survival. It could be shown that transplantation into the liver and into the lung in both systems (allogeneic and partially inbred) was accompanied by longer survival of the islets compared with the following regions: subcutaneous tissue, muscle, epididymal fat tissue, peritoneal cavity. This indicates that not only immunological but also factors of blood supply (oxygen consumption? ) play a role in the survival of the grafts. - The success of transplantation depends mainly on histocompatibility. Partially inbred rats showed significantly longer survival of islets than non-inbred rats. The studies of other groups using similar experimental models are reviewed.