Abstract: Within 0.5～1 hour after administration of ³H-pyquiton to mice infected with Schistosoma japonicum at a single dose of 100 mg/kg, the radioactivity levels of the worms reached maximum, but declined markedly 4 hours later In vitro, the uptake of ³H-pyquiton by bisexual worms maintained in cultural medium was also prompt. Moreover, the radioactivity levels of the worms increased with the concentrations of the drug.It was demonstrated that the labelled pyquiton absorbed initially by the schistosome was fat-soluble, and was metabolized gradually in the worms and transformed into water-soluble metabolites.Autoradiography showed that ³H-pyquiton entered into worms by simple diffusion mechanism and distributed in musculature, parenchyma, reproductive system and epithelial cells of the intestine. Maximum radioactivity was observed in the vitelline gland of female worm, and minimum in the testes of male schistosomes.