The pseudophyllidean tapeworm, Triaenophorus nodulosus, was found in 51% of the adult white bass, Morone chrysops, sampled from western Lake Erie during the summer of 1973. Prevalence of infection with Triaenophorus increased with size and age of fishes. This worm is responsible for the disease triaenophoriasis, which is grossly characterized by large, white cysts, dark-brown “streaks” and hemorrhages in the liver. Microscopically, there is an acute inflammatory response, necrosis of liver parenchyma, squamous metaplasia, fibrosis and displacement of liver tissue as the tapeworm grows. Many plerocercoids were necrotic and surrounded by a dense tissue. The pathophysiology of extensive liver obstruction needs to be investigated as well as its effect upon infected fish populations.