Two simple, rapid, and reproducible techniques of pancreatic tissue preparation produced favorable results after just part of the gland was autotransplanted in totally pancreatectomized animals. It is probable that the short and less traumatic treatment in vitro was responsible for the sufficient yield of viable islets. Moreover, the results show convincingly that the complete separation of endocrine from exocrine pancreas is not mandatory to insure adequate endocrine secretion. The spleen, an organ of no vital importance having a rich blood supply and belonging to the portal circulation, was a very suitable experimental implantation site, which permitted thorough evaluation of the tissue preparation techniques. These favorable results were not conditioned by the splenic tissue itself, because similar results have been obtained in dogs when the tissues were implanted into the liver via the portal vein.