Abstract: Germinal cells isolated from Echinococcus granulosus cysts harbored in mice have been maintained in an in vitro culture system containing RPMI 1640 supplemented by 20% calf serum, and used as a model for screening antihydatid drugs. When the germinal cells were maintained in the medium for 6 days, the cell proliferation rate was rather high in the first four days but declined in the last two days. In screening drugs, 1. 4× 106 germinal cells were exposed to known effective drugs against metacestodes of E. granulosus in mice, such as mebendazole (Meb) ,albendazole (Alb) or praziquantel(Pra) at various concentrations. One to three days after exposure, cell counts were made daily in 3 samples of each drug concentration. The mean cell number of each group was compared with that of the control and the inhibition rate of the cell was then calculated. The results showed that the minimal effective concentrations of Meb, Alb and Pra, were 1. 0(48h),2. 5(24h)and 10. 0(72h)μg/ml, respectively,while the inhibition rates of the cell were 34. 1,55. 7 and 18. 5%. Interestingly, the in vitro effects of Meb, Alb and Pra were consistent to those obtained from the in vivo tests, ie MebAlbPra. Nevertheless, after exposure of germinal cells to Meb at 2. 5μg/ml for 24h, the cells appeared in roughness, indistinction, shrunk or swelling, collapse, deformation and hole - like feature detected by light microscopy and scanning electron -microscopy , while the ultrastructure alterations of the cells noted by transmission electron -microscopy were lysis in cytoplasm, disruption or disappearance of nucleus and even darkness of the whole cell.Another 11 kinds of compounds included fenbendazole, flubendazole and oxibendazole had been passed through the abovementioned in vitro system. Only the drugs (such as fenbendazole, flubendazole and E8824) exhibited effect against hydatid cyst in mice also showed the in vitro effect on the germinal cells.The good correlation between the in vitro and in vivo tests indicates that the in vitro system may be used for screening antihydatid drugs.