The infection of Metagonimus yokogawai has been known to be present nationwidely and endemic in some parts in Korea. In order to select a highly effective compound against Metagonimus infections, the therapeutic effects were observed in 156 cases who were treated with several anthelmintic i.e. bithionol, niclosamide, niclofolan and praziquantel. All of the above drugs showed highly effective to the treatment of metagonimiasis by a single or two medication days. The egg reduction rates were in the range of 80.2 to 100 per cent. However, relatively low cure rates(8.3 to 37.5 percent) were observed in the groups treated by two doses of 30 mg/kg of bithionol, a single day treatment with 100 mg/kg of niclosamide and two doses of 1.0 mg/kg of niclofolan. On the other hand, the high cure rates were observed at the following dose rates of each drugs, i.e. the cure rate of 66.7 percent was obtained at two doses of 100 mg/kg of niclosamide, 88.9 percent of cure rate was observed at two doses of 2.0 mg/kg of niclofolan and a single dose of 10 and 20 mg/kg of praziquantel were shown as 85.0 percent and 88.0 percent of cure rates respectively. But the complete radical cure was obtained in the group treated by two doses of 20 mg/kg of praziquantel in 10 metagonimiasis cases. From the above results praziquantel was shown as the most highly effective against metagonimiasis and it was well tolerated without any side effect. Therefore, praziquantel is a very promising drug for mass treatment against metagonimiasis.