Abstract: The changes of Cysticercus cellulosae treated in vitro with pyquiton were studied under the transmission and scanning electron microscopes. They were also compared with normal controls. The detachment and adhesion of microtriches on the neck of their scolex were demonstrated under scanning electron microscope and numerous vesicular structures were seen on the surface of their neck. The vacuolization of their tegument, swelling of muscles and finally, destruction of their tissues were seen under the transmission electron microscope. It is indicated that pyquiton has a direct destructive effect on the parasite.