Type 1 diabetes in man and the NOD (H-2g7) mouse is frequently associated with an autoimmune response to two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67. GAD-specific autoantibodies produced by B cells and GAD-specific T cells have been observed in both species. In the current study, the response to a GAD65-derived peptide, GAD65 524-543, previously reported to be an epitope recognized by spleen cells obtained from 3-week-old NOD mice, was assessed in NOD MHC and non-MHC congenic strains. Although spontaneous reactivity to GAD65 524-543 was not observed in NOD mice, the peptide was immunogenic in NOD mice as well as in two NOD congenic strains which are both H-2g7, B10.H-2g7 and NOD.B6Il2-Tshb. This was surprising since the B10.H-2g7 strain does not develop diabetes or insulitis and fewer than 3% of NOD.B6Il2-Tshb mice develop diabetes. The response to GAD65 524-543 was shown to be controlled by the MHC since neither the B10 nor the NOD.H-2b strain, both of which are H-2b, responded to the peptide. This study demonstrates that T cell responsiveness to GAD-derived peptides can be elicited in strains of mice that are resistant to the development of spontaneous diabetes, suggesting that peripheral tolerance to GAD is not associated with protection from diabetes.