There is considerable evidence that at least some cases of juvenile onset diabetes mellitus in humans are a result of viral infection. Viral-induced diabetes in mice may provide an experimental counterpart more similar to the clinical situation than chemical-induced diabetes. Our experiments in such mice indicate that islet transplantation is effective in ameliorating viral-induced diabetes and is encouraging for ultimate clinical application of islet transplantation to juvenile onset insulin-dependent diabetics. In addition, our results show that islets in ectopic sites outside of the pancreas are resistant to damage induced by primary viral infection. The mechanism of this resistance is obscure and will be the subject of future investigations.