Biosynthesis of the polyamines, putrescine, spermidine and spermine, is required for DNA synthesis and liver regeneration after partial hepatectomy. Chronic ethanol consumption impairs polyamine synthesis during the prereplicative phase after partial hepatectomy. To determine whether this delay in polyamine synthesis contributes to ethanol's inhibition of liver regeneration, the ability of supplemental putrescine to improve regeneration in ethanol-fed rats was tested. Chronically ethanol-fed rats and isocalorically maintained controls underwent partial hepatectomy and were injected intraperitoneally with saline or putrescine (0.03 or 0.30 mmol/kg) at 0, 4, 8 and 12 hr after partial hepatectomy. Rats were killed at 24, 48 or 72 hr, 1 hr after exposure to [3H]thymidine, so that DNA synthesis could be estimated. DNA synthesis was significantly inhibited in ethanol-fed rats treated with saline compared with saline-treated pair-fed controls. Supplemental putrescine did not affect DNA synthesis in pair-fed rats. In contrast, putrescine significantly improved [3H]thymidine incorporation 24 to 72 hr after partial hepatectomy in ethanol-fed rats. Intraperitoneal injection of putrescine (1.2 mmol/kg) at the time of partial hepatectomy increased hepatic polyamine concentrations for the first 6 hr after partial hepatectomy despite significantly inhibiting the activity of ornithine decarboxylase, the rate-limiting enzyme for polyamine synthesis, in both groups. Hepatic polyamine levels after putrescine injection were greater in ethanol-fed rats than in similarly treated controls. These data suggest that putrescine treatment triggers events that normalize DNA synthesis in ethanol-fed rats. These results confirm the hypothesis that ethanol's antiregenerative mechanism intimately involves inhibition of putrescine synthesis.