The effects of ethanol on DNA and protein synthesis of regenerating rat liver has been studied. A single dose of ethanol, when given either before, at the time or 1 h after the partial hepatectomy significantly inhibited the accelerated synthesis of ornithine decarboxylase protein which was used as a marker of protein synthesis. Ethanol seemed to inhibit the synthesis of ornithine decarboxylase at transcriptional level of protein synthesis and the inhibition appeared to be directly due to the presence of ethanol molecules. When rats were chronically fed with ethanol-containing liquid diet also the total protein synthesis was inhibited during the two first days of regeneration. In this experiment also the rate of DNA synthesis was greatly inhibited by ethanol treatment. The results show that the ethanol-induced inhibition of the synthesis of tissue macromolecules is ideally demonstrated in regenerating rat liver. Furthermore they suggest that this effect may be of importance in the progression of alcoholic liver injury.