The HLA restriction and epitope specificity of cytotoxic T lymphocytes (CTL) involved in recovery from influenza type B infection have not been extensively characterized. Here lymphocytes obtained from a healthy individual contained virus-specific CTL restricted by class I HLA molecules, HLA-A1, A2, B7 and B8, and the class II HLA molecules, HLA-DR1 and DR3. Four conserved viral epitopes were predicted from allele-specific motifs for peptides interacting with HLA-B8 and HLA-DR1. Bulk CTL recognized three 9mer HLA-B8-restricted peptides from nucleoprotein, residues 30-38, 263-271 and 413-421, and a 13mer HLA-DR1-restricted peptide from hemagglutinin, residues 308-320. The epitopes presented by HLA-A1, HLA-B7 and HLA-DR3 remain undefined. Peptide-specific CTL lines recognized influenza type B virus-infected cells indicating the peptides are representative of naturally processed epitopes. A hemagglutinin peptide-specific CD4 CTL clone expressed approximately 200 molecules of perforin mRNA/cell, suggestive of a functional perforin pathway for target cell lysis. The results indicate a broad CTL response composed of both CD8 CTL and CD4 CTL recognizing viral epitopes presented by multiple HLA molecules.