A 4-year study on the factors affecting the prevalenee and epidemiological pattern of schistosomiasis japonica around Dongtin and Boyang lakes was reported. A proposal was made on the division of the endemic areas of the lake and marshland regions into different types,a definition about the high-risk places and the principles of their classification.This study also elucidated the main reservoirs of different types of endemic areas and the relationship between human exposure and infection. On the basis of the effects of prevention and treatment and cost-effect analysis in the 8 field study units, the goal for the control of schistosomiasis in the lake region for the next 3~5 years has been devised.A preliminary mathematical model of human and domestic animals as the main reservoirs of infection has been set up.