Many components that are derived from medicinal or dietary plants possess potential chemopreventive properties. Curcumin, a yellow coloring agent from turmeric (Curcuma longa Linn, Zingiberaceae), possesses strong antimutagenic and anticarcinogenic activities. In this study, we have found that curcumin inhibits the 12-Otetradecanoylphorbol-13-acetate (TPA)-induced nuclear factor κB (NF-κB) activation by preventing the degradation of the inhibitory protein IκBα and the subsequent translocation of the p65 subunit in cultured human promyelocytic leukemia (HL-60) cells. Alternatively, curcumin repressed the TPA-induced activation of NF-κB through direct interruption of the binding of NF-κB to its consensus DNA sequences. Likewise, the TPA-induced DNA binding of the activator protein-1 (AP-1) was inhibited by curcumin pretreatment.