RESUMO
An endemic dermatitis of unknown etiology has occurred among farmers working in paddy fields in the eastern area of Saitama Pref. In view of the results of the epidemiological and clinical observations, it was anticipated that the dermatitis might be caused by a bird schistosome (Ozu <I>et al.</I>, 1972).<BR>Thus, the research for snail intermediate hosts was carried out in the paddy fields as well as in the laboratory. Snails from the fields were placed in containers in which they could be checked for the shedding of cercariae. As a result, a species of furcocercous cercaria was obtained from <I>Austropeplea (Lymnaea) ollula</I>. The cercaria was identified as species belonging to the genus <I>Trichobilharzia</I> on the basis of the flame cell pattern, the behaviour, the responses to light and the detailed morphology of living and preserved specimens.<BR>In order to determine the dermatitis-producing properties of the cercaria, an experimental infection with the cercaria into the human skin was performed.The cercaria invaded into the human skin and produced a dermatitis quite similar to that prevailing in the endemic area.<BR>On the basis of the results from this study, the paddy field dermatitis occurring in the eastern area of Saitama Pref.was proved to be caused by the invasion of the cercaria belonging to the genus <I>Trichobilharzia</I> into the human skin.It was also proved that <I>A.ollula</I> served as the snail host of the cercaria.