To clarify whether the non-obese diabetes prone (NOD) mouse has an unusual pancreatic sensitivity to damage, mice were administered streptozotocin in high dose (direct beta cell toxic) or multiple low-dose (autoimmune-insulitis generating) regimen. NOD mice were found to be less sensitive to the diabetogenic effects of high-dose streptozotocin than C57BL/6 mice, but were exquisitely responsive to the multiple low dose regimen when compared to C57BL/6 or C3H/HeJ mice. These results suggest that the basic defect in NOD mice resides in the immune system and that the NOD mouse may be a useful model to investigate the relationships between environmental factors and intrinsic genetic predisposition to diabetes.