The gills of bottom-dwelling, territorial marine fish, oyster toadfish (Opsanus tau), from the lower York River, Virginia, were examined for histological alterations. Ten fish were collected from a location receiving industrial and sewage effluent. Common alterations (number of fish with lesions is given in parentheses) observed were telangiectasis (3), epithelial hypertrophy (4), alterations in chloride cell structure (5), deformed cartilage (4), focal inflammation characterized by lymphocytic infiltration (5), fibrinoid accumulations between the lamellar epithelium and the sinusoid (3), and proliferation of unidentified unicellular glands (4). In addition to the above mentioned lesions, granulomas in gill cartilage (2), deformed filament (2), epithelial hyperplasia arid fusion (1), arid thyroid hyperplasia in filaments (1) also occurred. The nature and the distribution of the fibrinoid in gill lamella will be discussed.