The effect of chronic ethanol administration on the incorporation of 3H-thymidine into DNA of isolated intestinal cells in the rat was investigated. Chronic ethanol consumption increased significantly DNA synthesis in intestinal mucosal cells. Whether this enhancement of DNA synthesis as a measure for cellular regeneration is due to the local effect of ethanol via tissue injury, to a direct stimulatory effect of ethanol on enzyme activities involved in DNA metabolism or to a change in the intestinal cell population with a shift to immature crypt cells by ethanol is not known.