A dry powder of betel nuts, piper betel leaves and lime was administered to rats. Epidermal thickening was frequently observed in the upper digestive tracts of rats in groups fed the betel nut diet mixed with lime and the betel leaves diet, and a forestomach papilloma was seen in 1 rat given betel leaves diet. These epidermal changes were scarcely seen in rats given either betel nut or normal diet alone.