Abstract: The effect of a single-dose oral administration of pyquiton on the tegumental sur face of adult Schistosoma japonicum in infected mice (C57/BL) was studied by SEM. Worms were recovered from mice 6,12,24 and 48 hrs after treatment, respectively. Pronounced tegumental surface alterations were observed including swelling, wrinkling and constriction, collapse of sensory bulbs, erosion of large areas of the surface. Different types of lesions with different degrees of intensity were described among worms from the same individual host.