The proliferative responses of UV-irradiated islets from fetal pancreas decreased to 53.8 +/- 4.7% (mean +/- SEM) compared to that of UV-irradiated islets by allogeneic mixed islet-cell lymphocyte culture. In 5 pancreatectomized dogs, UV irradiated fetal dog pancreas was transplanted either into omentum pouches or the spleen without immunosuppressive agents. The diabetic status (daily insulin requirement for hyperglycemia, decrease in body weight, urine glucose) improved in dogs after allo-transplantation. The survival time after total pancreatectomy was significantly longer in allografted dogs than those treated only with daily insulin injections.