We investigated the biological features of gastric surface mucous cell line GSM06, established from transgenic mice harboring the temperature-sensitive simian virus 40 large T-antigen gene. GSM06 cells grew until confluent monolayers were formed at the permissive temperature (33 °C), showing that the cessation of cell growth may be due to contact inhibition. Moreover, the cells did not grow in a soft agar gel. However, chromosome numbers of the cells were not normal. When GSM06 cells were cultured in Daigo’s T medium supplemented with growth factors and 10% fetal bovine serum at 33°C for 1, 3 or 9 days, the cells gradually grew to confluent monolayers (day 9). Morphological observations revealed that the cells time-dependently formed microvil-li-like structures and yielded periodic acid-Schiff-positive glycoproteins on the cell surface with the growth of the structures. When GSM06 cells were cultured on a membrane filter for 1-9 days, elevated transepithelial resistance was noted in a culture period-dependent fashion. On day 9, junctional complexes such as tight junctions and desmosomes were observed between the cells. In addition, prostaglandin E2 production was evoked from the cells from day 1. In order to determine cell viability, GSM06 cells were labeled with the fluorescence dye 2´7´-bis(carboxyethyl)-carboxyfluorescein. Exposure of GSM06 cells to ethanol (7.5-17.5%) elicited cell injuries in a concentration-related manner on day 1 whereas these cytotoxic effects were attenuated on days 3 and 9, suggesting that this protection may be, at least in part, related to the increased glycoproteins and transepithelial resistance. GSM06 cells possessing these unique characteristics should be highly useful as an in vitro model of gastric epith