Liver and serum xanthine oxidase(XOD) activity were determined in rats treated with DL-ethionine. Concomitantly, the enzyme activity was compared with that of rats treated with CCl$_{4}$, actinomycin D and those fed a protein depleted diet. The activity of XOD in liver was inhibited by injection of ethionine to the rats. But, there were no differences in activity of serum XOD between control group and ethionine-treated rats. And the pattern of changes in enzyme activity of serum and liver in ethionine-treated rats, was similar with actinomycin D treated rats or those fed a protein depleted diet. On the other hand, the activity of XOD was rather elevated both in serum and liver by injection of CCl$_{4}$ to rats.