Since fall 1996, fishermen working the waters of the lower Pocomoke River near Shelltown, Maryland have observed an increased frequency of external lesions on fish caught in their traps and nets. These lesions occurred on a variety of species with gross appearances ranging from mild focal petechiae to large, ulcerative, necrotic wounds. In August 1997, two fish kills were reported in the waters of the lower Pocomoke in the vicinity of Shelltown. Subsequently, these two fish kills have been associated with blooms of a toxic dinoflagellate(s) of the Pfiesteria complex. Juvenile Atlantic menhaden (Brevoortia tyrannus) were the primary species involved in each of the fish kills. According to surveys conducted by the Maryland Department of Natural Resources, approximately 90% of menhaden sampled from trawl nets along the affected stretch of the river during and following the fish kills had gross lesions. These lesions were varied, but predominantly appeared as circumscribed areas of hyperemia, dermal erosion, and tissue sloughing over the epaxial, abdominal, peri-anal, or caudal regions. Lesions often appeared to penetrate deeply into the underlying musculature with necrotic tissue debris protruding from the wound. Histologically, these lesions showed evidence of necrotizing dermatitis and myositis with floccular degeneration of skeletal muscle. Severe chronic granulomatous inflammation with hemorrhage, extensive tissue infiltration by lymphocytes and mononuclear cells, and multinuclear giant cell formation were also apparent. Where the lesion had penetrated to the abdominal cavity, abdominal organs were often involved; otherwise, involvement of other organ systems was limited. Aseptate fungal hyphae were evident throughout the lesions, particularly in association with granuloma formation. Appearance of these lesions both grossly and histologically bears remarkable similarity to lesions found in association with a disease syndrome involving Saprolegniaceae fungi (epizootic ulcerative syndrome, red spot disease, mycotic granulomatosis, ulcerative mycosis) and affecting a number of fish species, including Atlantic menhaden, throughout South and Southeast Asia, Australia, and the mid-Atlantic United States. Although lesions from the Pocomoke menhaden are thought to be associated with acute epizootics involving the toxic Pfiesteria complex, the chronic nature of the lesions described implies no direct relationship with ongoing blooms of toxic dinoflagellates.