The effects of selenium supplementation on azoxymethane-induced intestinal cancer were studied in male Sprague- Dawley rats given 8 weekly injections of azoxymethane (8 mg/kg body wt), and fed a 30% beef fat diet. Selenium-supplemented groups received 8 ppm H2SeO3 in drinking water. Blood selenium levels of supplemented rats increased rapidly the first 9 weeks of the experiment, followed by a plateau significantly higher than that for non-selenium controls. There was a significantly increase in liver and intestinal selenium levels in supplemented groups. The average number of intestinal tumors was 6.5 in the control group, and 3.1 in the selenium-supplemented group. There was a significant reduction in tumor incidence in the proximal half of the colon of selenium-treated rats. There was also increased concentration of tissue selenium in the proximal half of the colon of these rats.