Betel quid chewing is a general behavior in Taiwan, India, southeastern Asian and South Africa. In this study, microculture tetrazolium test (MTT) showed that the extract of lime-piper betel quid (LPB) (1.0-20 mg/ml) was toxic to JB6 cells. Cells exposed of LPB (0.1, 0.5, 1.0 mg/ml) for 7 days resulted in changes in cytomorphology with characteristics of carcinogenesis. With a long-term treatment (approximately 30 days) of low doses of LPB (1, 5, 10 microg/ml), the production of H2O2 and the activity of myeloperoxidase (MPO) and ornithine decarboxylase (ODC) were increased in JB6 cells. Cell cycle analysis showed a decrease in the G1 phase and an accumulation in the S phase 48 h after LPB treatment. When treating with 0.5 mg/ml LPB for 15 days as a promoter, type III foci were formed in the JB6 culture. These results demonstrated the tumor promotional effect of LPB in JB6 cells.