Approximately 25% of mature T cells possess two distinct cytoplasmic T cell receptor (TCR) α-chains, due to productive gene rearrangements of both alleles. Expression of two different α-chains at the cell surface is a potential risk factor for development of autoimmunity. However, it has been difficult to determine the frequency of peripheral T cells with two different α-chains at the surface. Our new approach is based on comparing by flow cytometry the percentage of cells that express a given Vα-chain between wild-type mice and mice that are hemizygous for a disrupted Tcra locus (Tcra+/−) and consequently unable to express two rearranged Tcra genes. We consistently found that ∼8% of total peripheral T cells express two surface α-chains. The importance of dual α-T cells in autoimmunity was examined in a mouse model for rheumatoid arthritis, namely collagen-induced arthritis (CIA). No significant difference was observed between Tcra+/− mice and wild-type littermates, considering arthritis incidence, day of disease onset, and maximum arthritic score. We therefore conclude that there is incomplete phenotypic allelic exclusion in TCRα, and that the presence of a significant number of potentially multireactive T cells does not increase the susceptibility to develop autoimmune arthritis.