To evaluate the effect of cyclohexane(CH) treatment on the serum levels of glutathion S-transferase(GST) activity in liver damaged animals, damaged liver was induced with pretreatment of 50% $CCl_4$ dissolved in olive oil (0.1 m1/100g body weight) intraperitoneally 17 times every other day. To $CCl_4$-treated rats, CH (1.56 g/kg body weight, i.p) was injected once and then the animals were sacrificed at 4 hours after injection of CH. The $CCl_4$-treated animals were identified as severe liver damage on the basis of liver functional findings, 1,e, increased serum levels of alanine aminotransferase(ALT), alkaline phosphate(ALP) and xanthine oxidase(XO) activities. On the other hand, $CCl_4$-treated animals injected with CH once($CCl_4$-pretreated animals) showed more decreased serum levels of ALT and XO, and more increased those of ALP rather than $CCl_4$-treated animals. In case of comparing the GST with ALT activity in liver, both $CCl_4$-treated and pretreated animals showed similar changing pattern of enzyme actvity. Especially $CCl_4$-pretreated animals showed significantly increased serum level of GST actvity compared with the $CCl_4$-treated those, whereas those of ALT showed reversed tendency. In aspects of GST enzyme kinetics, $CCl_4$-pretreated animals showed higher Vmax of liver GST enzyme than $CCl_4$-treated animals. In conclusion, injection of CH to the liver damaged rats led to enhanced liver damage and more increased activity of serum GST which may be chiefly caused by the enzyme induction.