Iron is excluded from foci of hepatocellular alteration in carcinogenesis of rodents and some fish. Among white perch (Morone americana), there is a condition of hepatic copper storage in which copper-loaded livers are produced naturally. In a group of fish collected from the Chesapeake Bay, Maryland (USA), from September to December 1990, we observed hepatic lesions which excluded copper similar to the phenomenon of iron exclusion, in a white perch with over 3,600 micrograms/g wet weight hepatic copper. The lesions were of two types: one with cells morphologically different from normal hepatocytes and which had diminished to absolute exclusion of copper with the copper specific histochemical stain rubeinic acid, and a second with cells morphologically similar to normal hepatocytes which had only a partial exclusion of copper. Although the exact cause and nature of the lesions was not determined, intrinsic copper toxicity, environmental pollution, or a combination of these factors may have contributed to their development.