To provide a plentiful supply of pancreatic islets for future clinical transplants into diabetic patients, the authors have developed a simple and consistent method of isolation of porcine islets. Both in vitro and in vivo studies demonstrated that the islets were viable and functional. Xenotransplants of 1.5 x 10(3) - 2.5 x 10(3) of microencapsulated porcine islets into diabetic mice resulted in restoration of normoglycemia in 13 of 18 experimental animals for up to 10 months. A xenograft of 50 x 10(3) microencapsulated porcine islets into a spontaneously diabetic monkey normalized hyperglycemia for more than 150 days. This experiment indicated that the transplantation of encapsulated porcine islets has great potential as a clinical treatment in diabetes mellitus.