Technical Abstract: Plant-based diets and phytochemicals contained in plant-based diets are associated with decreased risk of cancer. Brassica species and broccoli in particular are associated with reduced risk of several important cancers. Selenium (Se) is an essential nutrient that is covalently bound in a number of different chemical forms found in plants. Broccoli accumulates Se many fold beyond the concentration of Se in the soil, and the chemical form of Se in broccoli is similar to the chemical form in high-Se garlic, a food with unique chemo-protective properties. Selenium from broccoli grown to accumulate >500 ug Se/g did not accumulate in rat tissues or increase glutathione peroxidase enzyme activity to the same extent as selenium salts or seleno-amino acids. Selenium from high-Se broccoli decreased the incidence of aberrant crypts in rats with chemically-induced colon cancer by over 50%, relative to controls. Se from high-Se broccoli also decreased the incidence of mammary tumors in DMBA-treated rats and tumor number and volumn in APCmin mice. These results suggest that because of its decreased retention and increased chemoprotective properties, high-Se broccoli may be a unique supplemental form of Se.