The in vivo effect of 1-praziquantel on the fine structure of Clonorchis sinensis was investigated by means of light microscopy and scanning and transmission electron microscopy. Adult worms were recovered from the biliary system of infected rats 36 hours after oral administering at a single dose of 300 mg/kg

and 48 tcurs at the dosts of 100 mg/kg bid. for consecutive two days

respectively. Light microscopy showed worms contracted and deformed

bubble-like materials of different size appeared on the body surface

and the structures of testes became unclear with many blank areas. Scanning electron microscopy showed knobs on surface of tegument swelled and fused

large patchs of tegument stripped off to expose the underlying tissues

ar d the crate-like lesions appeared on tegument after bubbles bursting. Transmission electron microscopy showed vacuoles formed along basal membrance

syncytiums and muscles degenerated and lysed in different degree.The results from light to electron microscopy level are agreeable

and demonstrate that 1-praziquantel is remarkable effective on Clonorchis sinensis

especially causing gross tegum ental damage to the worms