Despite the advent of insulin for clinical use in 1922, our ability to control hypergly­ cemia and prevent the long term sequelae ofthe disease remains limited. Thus normalization of the milieu interieur with physiologic responses of insulin and metabolites remains an elusive but critically important goal. The developing endocrine pancreas provides a model system that speaks to many challenges of the transplantation biologist. Thus the attempt to of vascularization, growth and development, immunologic toler­ recapitulate the ontogeny ance, and glucose responsive insulin secretory capacity of fetal islet tissue provides a tantalizing possibility to replace insulin secreting tissue in persons with diabetes. Studies of this tissue are