Objective   To explore the killing effects of high intensity focus ultrasound (HIFU) on the hydatid cysts of Echinococcus granulosus.    Methods   Totally 25 hydatid cysts with thin walls

in good texture and lesser than 50 mm in diameter

were selected from fresh sheep livers

and divided into 5 groups by the stratified sampling method. The control group was treated by common ultrasound. The experimental groups were treated with HIFU at a sound power of 100

150

200 and 250 W respectively by multilayer circular radiation around the cyst wall. The instant death rates of protoscolecesin the treated cysts were investigated by trypan blue exclusion assay. The activities of lactic acid dehydrogenase (LAD)

alkaline phosphatase (AKP) in the cyst fluids were detected.    Results   The instant death rate of protoscolecesin the cysts was increased significantly with the elevation of sound power of HIFU (F=38.00

P0.01). The activities of LAD in the treated groups were higher significantly than those in the control group (F=14.75

P0.01); The activities of AKP in the treated groups were higher significantly than those in the control group (F=12.00

P0.01).    Conclusion   The multilayer circular radiation of HIFU is effective to injure hydatid cysts of Echinococcus granulosus.