The progressive morphological changes to early stage Taenia solium cysticerci following the treatment of pigs with a single therapeutic dose of oxfendazole (30 mg/kg), are described. On Day 1 after treatment, no obvious changes occurred in the general appearance of the larvae but alternations were seen by electron microscope, with an apparent reduction in the number of microtriches, and a complete disappearance of the tegument. Numerous granules were seen to have accumulated in the tegument cells. As treatment progressed, damage to the cysticerci was more serious and, by five days, all cysticerci were seen to be in an advanced stage of degeneration. By 45 days post-treatment, all cysts were calcified. These results suggest that oxfendazole is a highly effective drug against T. solium cysticerci in the early stages of development.