Four-week-old striped bass larvae were exposed for 24 h to 60, 80, 110, or 150/zg Cu++/L prior to an examination of their corneas by light and electron microscopy. Epithelial cells were sloughed from the corneas in a dose-dependent manner; corneas from fish exposed at the highest concentration were so denuded that the stromas were exposed. Corneas from fish exposed to 80 and 110 μg/L also exhibited a second type of pathological response that was concentration-dependent and resulted in greatly enhanced cytoplasmic density, condensed nuclear chromatin and pyknosis, extensive cytoplasmic vacuolation, and mitochondrial swelling and degeneration in the epithelial cells. Copper-induced pathological changes of the visual system may affect the ability of larvae to feed and to respond normally to visual stimuli.