To study the effect of bifidobacteria on preventing allergy response, levels of IFN-$gamma$, IgG2a, IL-4, and IgG1 were investigated in splenocytes isolated from ovalbumin (OVA)­sensitized allergic mice and BGN4-administered allergy­suppressed mice in the presence of various bifidobacterial strains. Most of the bifidobacteria, except 2A, increased production of Th I-associated immune markers, IFN -$gamma$ and IgG2a. In addition, most of the bifidobacteria, except 2A and 19A, decreased production of IL-4, whereas the differences in the production of IgG1 were less pronounced. These results suggest that some strains of bifidobacteria may have the potential to prevent the occurrence of allergy by switching Th1/Th2-type antibodies and/or related cytokines.