Abstract: Some histochemical changes in adult C. sinensis collected from rats infected artificially and treated with pyquiton were observed.1 h after administration the glycogen content showed a slight decrease which bscame prominent 24h later and almost disappeared at 48h post-medication. There was an increase in protein content in the parenchymal tissues of worms lh after treatment, especially in the reproductive organ 24h after treatment. RNA content was decreased lh post administration and continued decreasing gradually so that very little aould be seen 48h later. An increase in the activites of SDH, MDH and Ca-ATPase was seen at the beginning and became marked 24h after medication, while that for G-6-PDH was dtt-cted 48h after drug administration (Figs.1a-6b).No obvious changes in DNA, lipid, AKP, ACP and phenolase were detected within 1-48h after treatment.