Cyclophilin B (CypB) possesses two antigenic epitopes (CypB84–92and CypB91–99) recognized by HLA-A24-restricted and tumor-specific cytotoxic T lymphocytes (CTLs). To determine the safety of CypB-derived peptides and its ability to generate antitumor immune responses, patients with advanced lung cancer received subcutaneous vaccinations of these peptides or their modified peptides. All 16 patients were vaccinated with CypB91–99or its modified peptide, whereas only two patients were vaccinated with the modified CypB84–92, as immediate-type hypersensitivity to CypB84–92or its modified peptide was observed in the remaining patients. No severe adverse events were associated with the vaccination. No significant increase in cellular responses to either peptides or tumor cells was observed in the postvaccination PBMCs by the conventional CTL assays in any patients tested. These results suggest that the vaccination of CypB91–99peptide was safe, but failed to induce objective immune responses at this regimen.