OBJECTIVE Epidemiological and experimental studies have shown that dietary fiber may prevent colon cancer. Resistant starch, like dietary fiber, is not subject to digestion in the small intestine. However, it is unknown whether resistant starch inhibits colonic carcinogenesis. In vitro studies have shown that butyrate slows the growth of cultured colon cancer cells. The effect of resistant starch diet on 1,2-dimethylhydrazine-induced colonic carcinogenesis in rats was evaluated, and the colonic butyrate concentration was measured. METHODS Sprague-Dawley rats were randomly divided into five groups that were fed diets containing no fiber, 3% cellulose, 10% cellulose, 3% resistant starch, or 10% resistant starch. Colonic carcinogenesis and butyrate concentration of colonic contents and feces in each diet group were compared. RESULTS Total cancer volume per rat in the 10% cellulose group was significantly lower than that in the basal group (109 +/- 54 mm3 and 247 +/- 83 mm3; P < 0.05), but the other groups showed no significant differences. The butyrate concentration in colonic content and in feces were higher in the resistant starch groups than in the cellulose groups. CONCLUSIONS The resistant starch diet increased butyrate concentration but did not inhibit colonic carcinogenesis. It remains doubtful whether butyrate inhibits the proliferation of colon cancer cells.