Since 1969, the Overseas Technical Cooperation Agency and the Ministry of Agriculture and Forestry of Japan have been planning an exploitation of rice fields in the northeastern lowland of Leyte Island, the Phylippines. However many difficulties lie in this plan because the above lowland is one of the most serious endemic areas of Schistosoma japonicum in the philippines.
Landform or topography including climate, ground water, and other natural environments cresting pathological complex of Schstosoma japonicum is studied and some problems are shown from the topographical viewpoint in the present paper.
The northeastern part of Leyte can be divided into seven physiographic provinces (geomorphic surfaces), by map-reading as follows : the mountain land, the hilly land, the upland plain, the fan-shaped confluent plain (subdivided into upper and lower), the delta plain and the coastal plain.
Paddy fields are found mainly on the delta, the lower fan, and parts of the coastal plain, where the land surface may easily become water-logged when flooded.
Then it is supposed these geomorphic surfaces will offer inhabitable conditions to the intermediate snail host, Oncomelania quadrasi.
The same relationship between the topography and the snails has been found and studied in the endemic areas of Japan (Kofu Basin and others).
In Leyte the endemic area will soon expand into the neibouring lands on the upper fan as well as on the lower fan plains, and even into the upland where no paddy field has ever been seen, when irrigation canals will be established and rice cultivations will be enforced on it.
It appears that any rice exploitation with careless controls will not promote the real welfare of the people in this area due to the spreading of Schistosomiasis fosi.

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