We studied the effects of acute and chronic ethanol feeding on hepatic regeneration in rats after partial hepatectomy and toxic liver injury produced by D-galactosamine. Ethanol, when administered as a single dose (6 g/kg), inhibited ³H-thymidine incorporation into hepatic DNA; this effect depended in part on the time of ethanol feeding after partial hepatectomy. Multiple ethanol feedings produced an even greater inhibition, which persisted for at least 48 hr after partial hepatectomy. Rats chronically fed ethanol for 30 days also failed to achieve a hepatic proliferative response to either partial hepatectomy or D-galactosamine-induced hepatitis, comparable with isocaloric pair-fed controls. These investigations suggest that there may be a certain metabolic state in the hepatocyte cell cycle that is most susceptible to the action(s) of ethanol; inhibition of liver regeneration by acute or chronic ethanol consumption may result in delayed recovery from prior or coincident liver injury.