Technical Abstract: Colon cancer is the third most common newly diagnosed cancer in the United States and the third most common cause of cancer-related deaths. Previous supplementation studies have established the efficacy of selenium (Se) for prevention of colon cancer in humans. It is well established that the metabolism of Se depends on its chemical form, and studies have suggested that Se in broccoli is in a chemical form that does not accumulate in the body as fast as other forms of Se, and may be especially beneficial for prevention of cancer. In the present study, Fisher F-344 rats were fed diets containing adequate (0.1 ug Se/g diet) or supranutritional amounts of Se (1.0 or 2.0 ug Se/g diet) provided as selenate, selenite or high-Se broccoli, and injected with a chemical carcinogen (3,2 dimethyl 4-amino biphenyl or dimethyl-hydrazine). Supranutritional amounts of Se supplied as high-Se broccoli significantly decreased (P<0.05) the incidence of aberrant crypts (AC) and aberrant crypt foci (ACF; pre-neoplastic lesions indicative of colon cancer) as compared to other dietary treatments. Diets controlled for the presence or absence of broccoli and for the total amount of Se. The reduction in AC and ACF was a function of Se in high-Se broccoli and not a result of broccoli alone or Se alone. Adequate dietary Se supplied as high-Se broccoli did not accumulate in tissues or increase glutathione peroxidase activity as well as other forms and amounts of Se. Thus, Se from high-Se broccoli may be metabolized in a manner that diverts much of the Se into a pool that provides protection against colon cancer.