Pancreatic tissue from neonatal rats was cultured for 6 days and then transplanted into isologous animals made diabetic with streptozotocin. The cultured pancreatic tissue was implanted either into the peritoneal cavity or into muscle pockets and showed survival by functional and morphological studies for longer than 40 weeks. Pancreatic tissue from a patient subjected to subtotal pancreatectomy for chronic pancreatitis was maintained in culture for 7 days, with evidence for insulin release into medium, sterility, and histological viability of islets. Autotransplantation of this tissue into muscle pockets of the forearm was tolerated well. Glucose tolerance improved following transplantation, but evidence for function of the graft (insulin, C-peptide) remains inconclusive, 4 months after transplantation.