The etiology of halothane induced hepatitis is unknown. This study investigated effect of oral administration of Sho-saiko-to on hepatic injury induced by exposure to 1.1% halothane under hypoxic condition (FIO2 = 0.12) for 2 hr in rats. Serum transaminase, histological score and area of necrosis were examined in rats treated with Sho-saiko-to (900 mg.kg-1) before and after halothane exposure. Twenty-four hours following halothane exposure, serum transaminase levels were significantly depressed; the level of sGOT was significantly lower in rats with treatment of Sho-saiko-to (211 +/- 34 IU.l-1) than in rats without treatment (264 +/- 42 IU.l-1) (P less than 0.05), and the level of sGPT was significantly lower in rats with treatment of Sho-saiko-to (144 +/- 20 IU.l-1) than in rats without treatment (215 +/- 46 IU.l-1) (P less than 0.01). Histological score in rats treated with Sho-saiko-to was significantly lower (3.8 +/- 0.6) than in rats without treatment (4.5 +/- 0.7) (P less than 0.05). The area of centrilobular necrosis was significantly lower in rats with treatment of Sho-saiko-to (21.2 +/- 8.7%) than in rats without treatment (34.5 +/- 12.7%) (P less than 0.05), too. These results indicate that Sho-saiko-to inhibits the hepatic necrosis and functional disorder following exposure to halothane.