Nuclear factor kappa B (NF-kappaB) plays a wide variety of pathophysiological roles and modulation of its pathway can be a good novel drug target. Here, we found that our recently synthesized NF-kappaB inhibitor attenuated an ovalbumin-specific delayed-type hypersensitivity response in vivo and suppressed production of IL-12 by dendritic cells and TH1 cytokines by T cells in vitro. These findings suggest that the activation of NF-kappaB mounts TH1 type immune responses, and that this new NF-kappaB inhibitor has a therapeutic potential in this context.