Potent antigenotoxic and anti-tumor promoting activities of chlorophyll a from green tea (camellia sinensis) have been shown using in vitro cell culture experiments (Okai Y. et al. (1996) Mutation Res., 370, 11-17). In the present study, the authors analyzed in vivo effects of chlorophyll a and b from green tea on tumor promotion in mouse skin in the following ways. 1. When chlorophyll a and b from green tea were applied before each treatment by a tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on BALB/c mouse skin initiated by 7, 12-dimethylbenz [a] an-thracene (DMBA), they caused significant suppression in a dose-dependent manner against BALB/c mouse skin tumorigenesis. 2. Chlorophyll a and b showed significant suppressive effects against TPA-induced inflammatory reaction such as edema formation in BALB/c mouse ear skin in a dose-dependent fashion. These results suggest that chlorophyll a and b possess potent suppressive activities against tumor promotion in mouse skin.