Among 17 HLA-A2-positive healthy adults, CD8+ T-cell responses against an HLA-A2-restricted matrix protein 1 (M1) epitope increased after immunization with trivalent inactivated influenza vaccine (TIV) in two individuals. The presence of M1 in TIV was confirmed by Western blotting. T-cell cytotoxicity assays showed that TIV is processed and the epitope is presented by antigen-presenting cells to an M1 epitope-specific CD8+ T-cell line for specific lysis. These data show that TIV, which is formulated to contain surface glycoproteins to induce serotype-specific antibody responses, also contains M1, capable of inducing subtype cross-reactive CD8+ T-cell responses in some vaccinees.