Using a modification of the collagenase digestion, Ficoll gradient separation technique, we isolated the islets of Langerhans from fresh human pancreata removed from braindead cadavers. Comparison of the tissue insulin/amylase ratios between whole pancreas and isolated material revealed a significant purification of islet from acinar tissue. Also, islets isolated by this technique, when incubated in vitro, incorporated radiolabeled amino acid precursors into acid-alcohol-soluble islet proteins, thus indicating their viability and protein hormonal synthesis capabilities. Pig pancreata were processed by a similar technique, and the isolated material was transplanted to pigs with diabetes induced by total pancreatectomy. The mean survival time of the 11 pancreatectomized pigs that received an islet transplant was 15.3 days, while 13 pancreatectomized control pigs had a mean survival time of 6.0 days. Control pigs had no detectable circulating insulin 2 days after pancreatectomy. The pancreatectomized pigs that received an islet transplant, although remaining hyperglycemic, had insulin levels ranging from 5 to 14 μU/ml for up to 25 days after transplantation. The present studies demonstrate the feasibility of an approach designed for our ultimate goal-the large scale isolation and transplantation of islets in man.