An aqueous extract of betel-nut has been found to be able to induce strand breaks in DNA of mouse kidney cells in vitro. It has been also found to be able to enhance the rate of cell division at a dose of 100 micrograms/ml while a higher dose of 250 micrograms/ml was extremely toxic to the cells. Compared with arecoline (10 micrograms/ml), the aqueous extract of betel-nut seems to be a more potent carcinogen to mouse kidney cells in vitro.