We studied the effects of glucagon and insulin (GI) administration on the inhibition of liver regeneration by acute ethanol treatment after partial hepatectomy (PH) in rats. When ethanol was given 1 hour before PH at 3 gm/kg body wt., [3H] thymidine incorporation into the hepatic DNA 24 hr after PH was significantly inhibited, but it was completely reversed by GI treatment. Although hepatic ornithine decarboxylase (ODC) activity in the ethanol-treated group 4 hr after PH was significantly inhibited, it was completely reversed by GI treatment. The putrescine (PUT) level in the liver 4 hr after PH was decreased by ethanol, but it was increased by GI treatment. At 12 hr after PH, ODC activity was not inhibited and PUT level in the liver was not decreased by ethanol. The levels of spermidine and spermine in the liver 4 hr after PH were unaffected either by ethanol or by GI treatment. Spermidine/spermine-N1 acetyltransferase activity in the liver 4 hr after PH was showed a tendency to increase by ethanol but it was decreased by GI treatment. Difluoromethylornithine, a specific inhibitor of ODC, decreased the level of PUT in the liver, and inhibited [3H] thymidine incorporation. The intraperitotneal administration of PUT significantly increased [3H] thymidine incorporation. The increase in ODC mRNA caused by pH was inhibited by ethanol, but it was completely reversed by GI treatment. SAT mRNA was affected neither by ethanol ner GI treatment. These results suggested that GI treatment was effective on the inhibition of liver regeneration by acute ethanol treatment, and activation of liver regeneration by GI treatment is closely related with ODC induction at the level of transcription.