We have produced a T-cell receptor (TCR) transgenic NOD mouse, 6.9TCR/NOD, in which the expression of both diabetogenic T-cells and naturally occurring autoantigen were simultaneously controlled. The parent T-cell clone, BDC-6.9, and T-cells from 6.9TCR/NOD mice recognize a currently unidentified antigen present in NOD but not in BALB/c islet cells. A gene that codes for the antigen, or a protein that regulates the antigen, was previously mapped to a locus on chromosome 6. We have developed transgenic mice bearing the TCR α- and β-chains from the BDC-6.9 T-cell clone on a NOD congenic background in which the antigen locus on chromosome 6 of the NOD mouse is replaced by a segment from BALB/c. These NOD.C6 congenic mice lack the NOD islet cell antigen to which the BDC-6.9 T-cell clone responds. Diabetes in both male and female 6.9TCR/NOD mice is dramatically accelerated, but in 6.9TCR/NOD.C6 mice lacking the NOD islet cell autoantigen, we have not observed diabetes for up to 1 year of age. Thus, the generation of 6.9TCR transgenic mice provides a model of autoimmune diabetes whereby controlled expression of an endogenous polymorphic autoantigen effectively determines disease development.