A total of 44, 724 freshwater fishes of 18 species collected in the eastern Aomori Prefecrure for a period. from July 1992 to December 1995 were examined for the larvae ofGnathostoma nipponicum. Five fish species, Misgurnus anguillicaudatus, Silurus asotus, Chaenogobius urotaenia, Oncorhynchus masou, andTribolodon hakonensis, were shown to be infected and a total of 322 gnathostome larvae were detected and identified as the advanced third-stage larvae. Salmonidae and Cyprinidae fishes, includingO. masouandT. hakonensisrespectively, might be the more important as direct sources of human Gnathostoma infection in the northern part of Honshu, Japan.