Histological examination of over 6,000 oysters, Crassostrea virginica, inhabiting northern Gulf Coast estuaries revealed unencysted junvenile and possible adult stages of digenetic trematode, Proctoeces sp., inhabiting the gonadal ducts of the mollusc. The morphology of the worm is similar to juvenile stages of Proctoeces described in other bivalves. Infestation is highest in oysters from Mississippi Sound near Pascagoula, Mississippi with prevalence peaking in early winter and dropping off in spring and summer. The worm did not provoke a significant hemocytic response from the oyster. Oyster hemocytes were observed inside the digestive caeca of worms but there was no evidence of significant germinal feeding of gonadal impairment to the oyster. The hooked mussel Brachidontes recurvus, found attached to shells of oysters, may be significant in the life cycle of the digenean. The possibility of an altered life cycle in which the worm uses a surrogate host such as C. virginica in place of a vertebrate (fish) is hypotesized.