We recently reported that ventromedial hypothalamic (VMH) lesions produced an increase in DNA content in rat liver. In the present study, we examined the mechanism of increased hepatic DNA content produced by VMH lesions. Hepatic DNA content began to increase 3 days after VMH lesioning and continued to increase until 7 days after the lesioning. Hepatic DNA synthesis increased and reached maximum 3 days after the lesioning and then decreased to the initial level 7 days after lesioning. The increased DNA content and synthesis after VMH lesioning were completely inhibited by vagotomy (hepatic vagotomy or bilateral subdiaphragmatic vagotomy) and largely inhibited by the administration of atropine but not by administration of anti-insulin antibody. These results suggest that vagus firing produced by VMH lesions stimulates DNA synthesis in rat liver mainly through cholinergic receptor mechanisms.