An ovarian cancer patient was treated with human fibroblast interferon (HFIF) given daily by iv infusion, and the lymphocyte natural killer (NK) activity against K562 and the cytotoxicity against autologous tumor cells under various experimental conditions were investigated. After HFIF treatment, NK activity against K562 increased significantly, whereas the autologous tumor cell kill by lymphocytes was not increased with target tumor cells that were fresh, frozen then thawed, or frozen, thawed and cultured for 4 to 5 days before use. In vitro HFIF-stimulated lymphocytes also did not enhance cytotoxicity against the various autologous tumor cells. However, lymphocytes from allogeneic healthy persons did show enhanced cytotoxicity against cultured tumor cells of this patient after cultivation with HFIF, but had no significant effect against frozen tumor cells. Mixed lymphocyte-tumor cell reaction (MLTR) and MLTR-induced lymphocyte cytotoxicity against autologous tumor cells were not enhanced by HFIF. Thus, tumor-specific immune reactions directed toward autologous tumor cells were not enhanced by HFIF treatment under the conditions tested in this study.