A pilot experiment using NaPCP as a molluscicide to control schistosomiasis japonica was initiated in 1950--51 in Nagatoishi-cho, Kurume, Japan, where 1,050 persons lived behind dikes built to prevent flooding from the Chikugo River. They farmed 60 ha of rice, and 72.9% of them were infected with schistosomiasis. At the end of 2 years, 99.5% of the snails (Oncomelania h. nosophora) were controlled and new cases dropped from 30--35 per year to 5 and 0 at the end of the 1st and 2nd year, respectively. Mollusciciding was continued by Japanese, and paddy irrigation ditches were lined with concrete by 1958. Land reclamation, involving conversion of cultivated land in the river bottom to a golf course, resulted in virtual elimination of infected snails from this area and, when found, snails were uninfected. Using immunologic tests (intradermal, complement fixation, and circumoval precipitation) plus multiple stool examinations in 1972 and 1978, it was possible to demonstrate a marked decrease in cases of schistosomiasis in children 15 years of age or younger. These results were significantly different (P less than 0.001) from those found in similar tests run in 1940 and 1966. By 1978 all children in the Nagatoishi area of Kurume, Japan, were negative for Schistosoma japonicum infection.