The immunopathogenesis of autoimmune hepatitis (AIH), and the role of T cells in the onset and maintenance of this disease, are still unclear. Since T cells expand clonally after stimulation by an antigen, it is important to analyze the behavior of T cells at a clonal level. We have established recently a novel system, using reverse transcriptase-polymerase chain reaction (RT-PCR) and subsequent single-strand conformation polymorphism (SSCP) that allows the identification of clonal accumulation of T cells in a lymphocyte population. Using this system, we demonstrated that oligoclonal T cells were accumulated in the liver of patients with AIH, and that identical T-cell clonotypes were detected in two different regions of the liver, although these features were also observed in cases with viral hepatitis. Only in cases with AIH, however, nearly all identical T cells were found to belong to CD8+ subset and there were very few CD4+ T cells in this population. Our results suggest that common antigens presented to CD8+ T cells in the context of HLA class I molecule are distributed diffusely in the liver of AIH. These findings also suggest that antigens recognized by CD4+ T cells may be relatively heterogeneous in the liver with AIH.