Technical Abstract: Flow cytometry was used for quantitative evaluation of anti-tumor promoting activity by an in vitro short-term assay system measuring inhibition of Epstein-Barr virus early-antigen activation (EBV-EA) induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). This assays simultaneously measures both anti-tumor-promoting activity and cytotoxicity of target substances using the same batch of cells. Using this modified short-term procedure, we determined the anti-tumor promoting activity of 70% ethanol-water extracts of bran (outer layer) from seeds of five pigmented rice cultivars: JumLalocal-1, DZ 78, Elwee, LK1-3-6-12-1-1, and LK1A-2-12-1-1. The results show that compared to an extract from the nonpigmented white cooking rice variety Chuchung, the extracts from the pigmented varieties strongly inhibited phorbol ester-induced tumor promotion in marmoset lymphoblastoid cells B95-8 in vitro. The information should be useful for applying the short-term test of anti-tumor-promoting activities of rice bran to other natural products and for evaluating pigmented rice cultivars as a genetic resource for the development of health-promoting rice varieties.