Antitumor activities of OK-432-stimulated peripheral blood mononuclear cells (PBMC) were examined. Killer activity against natural killer (NK) cell-sensitive K562 as well as lymphokine activated killer (LAK) cell-sensitive Daudi and PC3 target cells were detected among PBMC cultured with a low dose (0.0125-0.05 KE/ml) of OK-432. Kinetic analysis of killer activity showed that it reached a plateau level by 48 h of culture. Various freshly isolated tumor cells from oral cancer patients were also lysed by both the autologous and allogeneic OK-432-stimulated PBMC (OK-MC), suggesting that the specificity of the killer was not restricted by HLA and was thus non-specific. Fluorescence activated cell sortor (FACS) analyses showed that CD57+/CD25+ and CD16+/CD25+ cells were increased in PBMC after 48-h stimulation with OK-432. The killer activity was further augmented by the addition of rIL-2 at the time of killer assay.Tumor growth inhibitory factor (TGIF) activity, which we previously reported, was found in the culture supernatant (CSN) of OK-MC from various cancer patients. The titer of TGIF from these patients was high enough, 16-64 × of the reciprocal dilution of the CSN, which was almost equivalent to the activity from normal healthy controls.These results suggest that two kinds of antitumor activities were induced in the OK-432-stimulated PBMC in vitro, the one being cell-mediated and the other lymphokine-mediated (TGIF). OK-MC is thus supposed to be effective for adoptive immunotherapy (AIT) in oral cancer patients.