Mustard seeds (MS), which are consumed in considerable amounts by the Japanese people that, interestingly, have the longest life expectancy in the world, are known to contain a number of yet not fully defined but quite powerful anti-oxidants. A suspension of extracted MS was found to suppress oxidized-LDL-induced macrophage respiratory burst in vitro, to prevent growth, and to induce apoptotic death of SW480 cells (a human colon cancer cell line), while no such effects were found for normal 3T3 cells. A diet enriched with MS decreased plasma levels of the lipid peroxidation product malonaldehyde in mice exposed to the colon cancer-inducer azoxymethane (AOM). Such a diet also dose-dependently enhanced the activity of several anti-oxidant enzymes, such as superoxide dismutase (SOD), catalase, and GSH-peroxidase and, moreover, reduced AOM-mediated formation of colon adenomas by about 50%. Further studies are required to detail and explore the beneficial effects of MS and their rich content of powerful anti-oxidants.