The effects of autonomic nervous system on liver damage induced by carbon tetrachloride (CCl4) and repair were investigated morphologically and biochemically in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). After repetition of CCl4 treatment twice a week for 4 weeks, the SHR showed liver cirrhosis histologically. In WKY, however, only fibrosis was observed. Biochemically, the serum glutamate-pyruvate transaminase (GPT), liver lipid peroxidation (LPO) and superoxide dismutase (SOD) activities were measured. CCl4 increased the activities of GPT and LPO but decreased that of SOD in SHR more than in WKY. These findings indicate that liver damage induced by CCl4 was more severe in the sympathetic hyperactive SHR than in the normally active WKY. In induced cirrhotic liver of SHR and fibrotic liver of WKY, diffuse serotonin particles and numerous mast cells were observed in the fibrotic matrix, and some neovascular adrenergic fibers were found in these areas. These results indicate that the sympathetic nerve can exacerbate the liver damage, and both mast cells or serotonin particles and sympathetic nerve participate at some stages in the repair of liver damage.