Segmental pancreatic allografts with unligated ducts were transplanted intraperitoneally to five diabetic patients who had received renal allografts more than 2 yr earlier. One patient is alive with a functioning graft 10.5 mo later. Two patients rejected their grafts at approximately 2 and 3 mo but are alive 8--9 mo later after resumption of exogenous insulin therapy. In both patients, carbohydrate metabolism was nearly normal during the period of graft function. Two patients died of infectious complications between 1 and 2 mo after transplantation. The main hazard of pancreas transplantation relates to the immunosuppression necessary to prevent rejection, setting the stage for infectious complications. Technically, pancreas transplantation is a feasible and efficient procedure, and, if better methods are developed for preventing rejection, it should be applicable to patients prone to develop secondary complications of diabetes.