Sprague-Dawley male rats, 24 days of age, were placed on diets based on a balanced ration as such and supplemented with Brazilian A rabica green coffee bean oil (0.10%), silymarin flavonolignans (0.10%), porcine trypsin (2429 mu/g ration) and ferrous sulfate (0.24% Fe) for a period of 32 weeks. A portion of the controls was switched to the iron salt diet at day 37 when 1,2-dimethylhydrazine was administered by gavage at a dosage of 20 mg/kg (base) and continued weekly for a total of 15 weeks. The colon and small intestinal adenocarcinoma numbers were determined for each group of rats surviving the carcinogen treatment and compared with the respective controls by a statistical design based on Poisson distribution. The results indicate that the adenocarcinoma frequencies of the colon, both total and occurrence in the proximal and distal portions were significantly decreased in the groups fed coffee oil, silymarin group and trypsin. The colon tumor numbers for the iron salt-fed were in the control range except for a decrement in the distal colon for rats on the diet from the start. Small intestinal adenocarcinoma scores with all supplemented diets did not differ significantly from the controls.