The effect of different dietary carbohydrates (sucrose, cornstarch and high amylose cornstarch) on intestinal carcinogenesis was studied in male Sprague-Dawley rats treated subcutaneously with azoxymethane (AOM) at a weekly dose of 8 mg/kg body wt for 8 wk. The diets, high in fat and low in calcium and fiber, were fed during and after AOM treatment. The number of colonic adenomas per rat in the groups fed either starch was lower (P < 0.05) than the number in the sucrose-fed rats [1.06 +/- 0.38, 0.30 +/- 0.10 and 0.41 +/- 0.22 (mean +/- SEM), in the sucrose-, cornstarch- and high amylose cornstarch-fed groups, respectively]. The incidence of total intestinal tumors (adenomas + adenocarcinomas) was not affected by dietary treatment. However, the incidence of tumors in the small intestine of the rats fed the two cornstarch diets tended to be slightly lower than for rats fed the sucrose diet (P = 0.075). Adenoma dysplasia and adenocarcinoma differentiation were similar among the rats fed the three diets. However, the adenocarcinomas in the rats fed the cornstarch diet were significantly smaller than those in the rats fed sucrose [0.99 +/- 0.14 cm2 (n = 13), 0.56 +/- 0.14 cm2 (n = 13) and 0.55 +/- 0.17 cm2 (n = 9) in rats fed the sucrose, cornstarch and high amylose starch diets, respectively]. Moreover, in the rats fed the cornstarch diet, the adenocarcinomas showed lower invasive potential than those in rats fed the sucrose diet. The results suggest an overall inhibition of AOM-induced carcinogenesis in rats fed the cornstarch diets.