Paragonimus westermani is an endemic disease and has had scattered distribution in Northern Taiwan for the long period of 108 years. In order to know the current status of the prevalence of this disease in Taipei County, an investigation by means of examination of snail, crab and stool for identification of cercariae, metacercariae and ova of Paragonimus westermani was carried out in five small highly endemic foci-Alilao, Shengkeng, Shuangchi, Shihjen and Taiping from July 1984 to June 1985. The results obtained are summarized as follows: The infection rate for 17, 412 fresh-water snails, Semisulcospira libertina, the first intermediate host and for 180 fresh-water crabs, Eriocheir japoniucs, the second intermediate host was both negative in the first four places. On the contrary, the rate for 879 fresh-water snails, Semisulcospira libertina, for 298 fresh-water crabs, Potamon miyazaki and Potamon dehaani and for 45 school-children was zero, 26.8% and zero respectively, in the last one. Based on the above findings, it is concluded that in the last 20 years, Paragonimus westermani might probably be under control in the former areas which are now developed districts. This development has probably influenced the prevalence and distribution of the disease. But it is still prevalent in the latter area located in remote undeveloped mountain.