NIH mice infected with Schistosoma japonicum cercariae for 3, 7, 14, 21 or 35 d were treated ig either with arteether or artemether at the daily dose of 100-200 mg.kg-1 for 2 d, the efficacy produced by both drugs was similar. The d 7 schistosomules and d 35 adult worms were more susceptible to arteether or artemether with respective worm reduction rates of 77.5%-87.2% and 51.7%-61.3%. Histological and histochemical studies showed that d 7 and d 35 schistosomes, harbored in mice treated with arteether 300 mg.kg-1.d-1 for 2 d appeared in cloudy swelling and vesiculation in the tegument, distension of intestine, apparent decrease or even disappearance of glycogen and inhibition of alkaline phosphatase activity in the tegument and parenchymal tissues, as well as formation of dead worm granuloma.