BACKGROUND Cytotoxic T lymphocytes (CTL) have been shown to be useful for adoptive immunotherapy in malignancy. Traditional sources for CTL, such as tumor-infiltrating lymphocytes, have limitations. It would therefore be useful to develop a method of generating antitumor CTL from a renewable source such as peripheral blood. METHODS DBA/2 mice were injected intradermally in the abdominal wall with the murine tumor PHS-5 and killed 14 days later. Peripheral blood lymphocytes were harvested and cultured with 20 units/ml interleukin-2 and autologous tumor-stimulator cells treated with mitomycin C. Cultures were split when greater than 2 x 10(6) cells/well, fed every 3 days and stimulated weekly. RESULTS Lymphocytes expanded greater than 130,000-fold during 8 weeks. Specific cytotoxicity was shown with 51Cr release assay. Withdrawal of repeated stimulation with autologous tumor resulted in failure of cells to expand in culture and loss of cytotoxicity. In vivo administration showed marked reduction of 10-day liver metastases, indicating therapeutic efficacy. CONCLUSIONS These data demonstrate a successful animal model of adoptive immunotherapy with CTL generated from peripheral blood lymphocytes.