Previous studies have shown that male rat liver undergoes demasculinization during hepatic regeneration after partial hepatectomy. In the present study the effect of the antiandrogen flutamide on liver regeneration was assessed. Adult male Wistar rats were treated with flutamide (2 mg/rat/day or 5 mg/rat/day subcutaneously) or vehicle for 3 days prior to and daily after partial hepatectomy. Rates of DNA and polyamine synthesis were assessed by measuring thymidine kinase and ornithine decarboxylase activities, respectively. The rate of liver growth after partial hepatectomy in the three groups was similar at all time points examined. The increases in thymidine kinase activity and ornithine decarboxylase activity after partial hepatectomy were comparable throughout the study. Thus, administration of flutamide did not influence the regenerative response after partial hepatectomy.