Polymyositis (PM) is an inflammatory muscle disease caused by autoimmune dysfunction, considered to be caused by cytotoxic CD8 T cells. To date, no autoantigens have been identified. We attempted to induce an experimental allergic myositis (EAM) in BALB/c mice by inoculating syngeneic dendritic cells (DC) presenting peptides that are expected to match the binding anchor motif of H-2K(d) (BALB/c). We selected peptides that are highly expressed in skeletal muscle. Only when we inoculated syngeneic bone marrow-derived DC presenting pyruvate kinase M1/M2 peptide 464-472 in BALB/c mice, 41.7% of the mice (EAM) developed pathological changes in skeletal muscle compatible to human PM. Under other conditions (when we inoculated DC presenting no synthetic peptides into BALB/c or C57BL/6 mice and DC presenting pyruvate kinase M1/M2 peptide into C57BL/6 mice), there were no necrotizing and inflammatory lesions. Induction of EAM in the same manner as above also induced CTL activity against P815 cells with the same peptide and syngeneic differentiated cultured myotubes without peptides by the chromium release assay. Consistent with the similarity of the binding anchor motif of H-2K(d) (BALB/c) and HLA A*2402, we conclude that pyruvate kinase M1/M2 peptide is a candidate autoantigen not only in BALB/c-EAM but also in human-PM with the HLA A*2402 allele.