Schistosoma japonicum were obtained from infected rabbits 24 hours after treatment with praziquantel at a single dose of 30,35,40 mg/kg. The drug-induced alterations of histochemistry of the worms have been studied.The results indicated that the glycogen content and AKP (alkaline phosphatase) activities of the worms decreased markedly or disappeared as compared with those of untreated worms; however, the activities of ACP (acid phosphatase) in both treated and untreated worms revealed no apparent change.