Three gilts fed a diet containing 100 mg fumonisin B1/kg for 7 days followed by a diet containing 190 mg/kg for 83 days developed nodular hyperplasia of the liver. These nodules of various diameters were composed of solid sheets or nests of hepatocytes. There were no discernible central veins or portal triads, and the perilobular connective tissue and adjacent parenchyma were compressed. Three other gilts maintained on the same diet for 27-80 days developed severe hepatopathies, but not nodular hyperplasia, necessitating euthanasia prior to conclusion of the feeding trial. At necropsy, 1 of the 6 gilts had grossly apparent hyperplastic plaques within the distal esophageal mucosa. On histopathologic examination, 6 of 6 gilts had mild to severe hyperkeratosis, parakeratosis, and formation of papillary downgrowths of the stratum basale of the distal esophageal mucosa. The hyperplastic nodules in the liver and the changes in the distal esophageal mucosa illustrate the unique chronic toxicity of this mycotoxin in pigs.