In the short span of 6 years, remarkable advances have been made in islet transplantation. Techniques have been developed which permit the successful reversal of the diabetic state in rats by transplanting isografts of either adult islets, dispersed neonatal pancreases or fetal pancreatic tissue. Islet transplantation prevents or reverses early microvascular complications of the diabetic state in animals. The immune barrier has been bent by simple in vitro procedures which apparently alter the passenger leucocytes of the islets and thus markedly prolong allograft survival. The safety of islet transplant procedures has been established in man. Hopefully, future investigations will continue the bending and lead to the breaking of the immune barrier so that it can be determined whether islet transplantation in man will prevent, arrest or reverse the microvascular, macrovascular and neurological complications that occur in the diabetic patient.