Ginseng is a well known traditional medicine in Asian countries which has attracted attention as a potential chemopreventive agent. In the present study, inhibitory effects of white and red ginseng on tumor development were examined using medium-term liver and multi-organ carcinogenicity bioassay systems. No modifying potential of the ginseng preparations were evident in terms of the numbers or areas of glutathione S-transferase placental form (GST-P)-positive foci in rat livers. However, white ginseng, although not its red counterpart, was found to decrease the incidences of adenocarcinoma of the small intestine and colon in the medium-term multi-organ carcinogenesis model, without any affect on the numbers of aberrant crypt foci (ACF). These results indicate that white ginseng may have inhibitory effects on the progression stage of rat intestinal carcinogenesis, but the influence is not strong. Ginseng did not appear to have promoting or inhibitory effects in other organs under the present experimental conditions. Possible application on ginseng for chemoprevention of colon cancer in humans, can be concluded given the lack of obvious adverse effects.