China represents the largest endemic area of S.japonicum infection.Geographically,the northernmost limit of the endemic area is at 33 45'latitude north,the southernmost at 21 43' latitude north,the easternmost at 121 45' longitude east, and the westernmost at 99 5'longitude east(Mao & Shao,1982).In 1948 the disease was present in 138 counties with more than five million inhabitants infected and a mean prevalence rate of 21.1% (Mao,1948). In 1955 it was estimated that approximately 10 million people were suffering from schistosomiasis,and that 100 million people were constantly exposed to the risk of infection (Pan,1957;Chien,1958).