Restricted use of T cell receptor (TCR) gene segments is characteristic of several induced autoimmune disease models. TCR sequences have previously been unavailable for pathogenic T cells which react with a defined autoantigen in a spontaneous autoimmune disease. The majority of T cell clones, derived from islets of NOD mice which spontaneously develop type I diabetes, react with insulin peptide B-(9–23). We have sequenced the α and β chains of TCRs from these B-(9–23)-reactive T cell clones. No TCR β chain restriction was found. In contrast, the clones (10 of 13) used Vα13 coupled with one of two homologous Jα segments (Jα45 or Jα34 in 8 of 13 clones). Furthermore, 9 of 10 of the Vα13 segments are a novel NOD sequence that we have tentatively termed Vα13.3. This dramatic α chain restriction, similar to the β chain restriction of other autoimmune models, provides a target for diagnostics and immunomodulatory therapy.