Since flaxseed ingestion produces potentially anticarcinogenic lignans in the colon, this study determined whether flaxseed decreases the risk for colon carcinogenesis. Following a single injection of azoxymethane (15 mg/kg body wt.), five groups of male Sprague-Dawley rats were fed a high-fat (20% corn oil) basal diet with or without supplementation with 5% or 10% flaxseed meal (FM) or flaxseed flour (FF) for four weeks. Upon sacrifice, colons were examined for aberrant morphology and cell proliferation. In the descending colon of supplemented groups, the total number of aberrant crypts and foci were significantly reduced by 41-53% and 48-57%, respectively. The labeling index (LI) was also 10-22% lower in these groups, except for the 5% FM group. While these effects are not linearly related to the level of flaxseed fed, it suggests that flaxseed feeding may reduce the risk for colon carcinogenesis.