The experiments described here were aimed at developing novel probiotic strains that may aid in the reduction of colon cancer risk. We assessed the potential anticancer properties of Lactobacillus acidophilus NCFMTM in male F344 rats using inhibition of the formation of azoxymethane (AOM)-induced aberrant crypt foci (ACF) in the colon as the measure of preventive efficacy. At 6 weeks of age, groups of rats were fed the experimental diets containing 0, 2% or 4% lyophilized cultures of L. acidophilus NCFMTM. At 7 weeks of age, all animals in each dietary group, except the vehicle-treated rats, were s.c. injected with AOM (15 mg/kg body weight) once weekly for two weeks. The vehicle-treated groups were given s.c. injections of normal saline. All rats were necropsied 10 weeks after the last AOM injection and ACF in formalin-fixed, methylene blue-stained colonic tissues were counted under the light microscope. The contents of the cecum were analyzed for bacterial beta-glucuronidase activity. Diet supplementation with the probiotic strain NCFMTM significantly suppressed AOM-induction of colonic ACF, in terms of total number, as well as crypt multiplicity and number of ACF/cm2 colon (P<0.01 - 0.001). NCFMTM inhibited AOM-induced colonic ACF formation in a dose-dependent manner (P<0.01). A significant dose-dependent reduction of cecal beta-glucuronidase activities was observed in the rats fed 2% (P<0.04) and 4% (P<0.0001) NCFMTM. These results suggest that Lactobacillus acidophilus NCFMTM may potentially prevent colon cancer development. Further studies are warranted to determine the full potential of this probiotic strain in preclinical efficacy studies.