The comparative susceptibility of rainbow trout Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch to the parasites Caligus flexispina (Copepoda) and Ceratothoa gaudichaudii (Isopoda) was studied. The land-based salmon culture was carried out in 8 m(3) tanks with independent and continuous sea water supply with two different densities and two replications at Bahia Metri (41 degrees 43'00 '' Lat. S., 72 degrees 36'30 '' Long. W). The copepod was found in 3 out of 4 tanks with rainbow trout with a prevalence from 14% to 83%, whereas a prevalence of 25% was found only in one tank with coho salmon. The isopod was present only in 2 of the 4 tanks with reared coho salmon with 28% and 29% of prevalence respectively. This indicates that C. gaudichaudii is an important parasite to the coho salmon and is unimportant to the trout. On the contrary, the coho salmon is more resistant to the copepod parasite. This is the first record of C. flexispina in cultured salmonids from Chile.