Two species of salmon (masu salmon Oncorhynchus masou and pink salmon O. gorbuscha) captured in the northern Sea of Japan during April 1990 were examined for infection by adult female salmon lice (Lepeophtheirus salmonis) to assess the relative importance of each to the parasite. Masu salmon had relatively low prevalence and abundance of infection and carried less than 4% of the estimated parasite population, indicating that masu salmon are utilized rarely by L. salmonis and may not be important hosts. In contrast, the infection level on pink salmon was higher, with pink salmon carrying more than 96% of the parasites found on the 2 salmon populations.