This study concerned the suitability of rainbow trout as an experimental host for plerocercoids of Triaenophorus crassus. Twenty-five trout were exposed to Cyclops bicuspidatus thomasi infected with procercoids of T. crassus. Plerocercoids were recovered from 11 of these fish. Hemorrhaging in the muscle was the first evidence of infection in live fish between Days 22-58 postinfection (PI). Migration of worms created extensive lesions in the muscle by Day 30 PI followed by formation of granulomas between Days 45-75 PI. One to three plerocercoids were wound throughout the muscle after Day 30 PI, and penetration into the body cavity and through the integument was common. Mortality of infected trout was first observed at Day 44 PI, and by Day 56 PI, 45% of the trout died. The swimming behavior of infected trout was marked by decreased activity and loss of equilibrium.