The role of the vagus nerve in liver regeneration after partial hepatectomy was examined by comparing the effects of hepatic vagotomy (sectioning of the hepatic branch of the vagus nerve) with those of subdiaphragmatic vagotomy in rats. Hepatic vagotomy delayed but did not suppress the increase in the rate of hepatic DNA synthesis and the activity of thymidine kinase after partial hepatectomy. On the other hand, subdiaphragmatic vagotomy delayed and suppressed these indices. The time courses of restoration of liver DNA content after partial hepatectomy were not affected by hepatic vagotomy. However, this index was both delayed and suppressed in subdiaphragmatic vagotomized rats. Hepatic vagotomy did not affect the daily food intake or the body weight increase after partial hepatectomy. However, subdiaphragmatic vagotomy caused considerably more loss of food intake and body weight. There were no differences in the plasma insulin levels after partial hepatectomy among three groups. We concluded that a vagal specific effect is evident in the delay but fails to suppress liver regeneration.