Colorectal cancer is a major cause of cancer deaths in Western countries, but epidemiological data suggest that dietary modi®cation might reduce these by as much as 90%. Cyclo-oxygenase 2 (COX2), an inducible isoform of prostaglandin H synthase, which mediates prostaglandin synthesis during in¯ammation, and which is selectively overexpressed in colon tumours, is thought to play an important role in colon carcinogenesis. Curcumin, a constituent of turmeric, possesses potent anti-in¯amma-tory activity and prevents colon cancer in animal models. However, its mechanism of action is not fully understood. We found that in human colon epithelial cells, curcumin inhibits COX2 induction by the colon tumour promoters, tumour necrosis factor a or fecapentaene-12. Induction of COX2 by in¯ammatory cytokines or hypoxia-induced oxidative stress can be mediated by nuclear factor kappa B (NF-kB). Since curcumin inhibits NF-kB activation, we examined whether its chemopreventive activity is related to modulation of the signalling pathway which regulates the stability of the NF-kBsequestering protein, IkB. Recently components of this pathway, NF-kB-inducing kinase and IkB kinases, IKKa and b, which phosphorylate IkB to release NF-kB, have been characterised. Curcumin prevents phosphorylation of IkB by inhibiting the activity of the IKKs. This property, together with a long history of consumption without adverse health e ects, makes curcumin an important candidate for consideration in colon cancer prevention.