A histopathological examination of parenchymal organs of the whitefish Coregonus albula (L.) infestcd with metacercariae of Cotylurus erraticus established the extent of inflammation and necrotic changes and justified a possiblity that the fish died as a result of the invasion. The examination revealed damaging inflammation of the cardiac muscle and retrogressive changes in the kidney vrith progressing damage of nephron elements, congestion, and hyperplasia of endoparenchyma of hemopoietic properties. The high pathogenicity of Cotylurus erraticus metacercariae is evidenced by the scope of necrobiotic changes resulting from mechanical damage brought about by penetration, encystment, and intoxication.