A total of 137 organic compounds were screened in the laboratory as potential molluscacides against Oncomelania nosophora, the amphibious snail host of Schistosoma japonicum. 9 of the best, or combinations of these, were tested in small field plots (9 sq. ft.). 4 of these[long dash]90% 2,4,6-trichlorophenol (Dowcide 2-S), 75% sodium pentachlorophenate (Dowcide G), 2,4,5-trichlorophenol, Na salt (Dowcide B) and Cu pentachlorophenate[long dash]were found to be effective. The first 2 gave 100% kill in 14 days, the 3d gave only 47%, while Cu pentachlorophenate gave 96%.