Because a restricted repertoire of T-cell receptor (TCR) Vβp gene expression has been reported in other autoimmune diseases, the possibility of similarly restricted Vα gene expression by T-cell infiltrates of NOD mouse islets was examined. With isolated islets from 4- to 12-wk-old NOD mice, a prospective polymerase chain reaction analysis with 18 Vβ-specific oligonucleotide primers was performed on the noncloned and unexpanded islet-infiltrating T cells. The methodology used permitted the detection of a minimum of 50 T cells. In contrast to the restricted TCR Vβ gene usage reported for other autoimmune diseases, infiltrates of even the youngest mice were characterized by expression of multiple Vβ gene segments.