For observing biochemical and morphopathological changes in experimental cerebrocortical necrosis, 6 sheep and 6 calves were given amprolium (600 mg/kg/day). All of the amprolium-dosed animals showed neurological signs and died on days 35 to 57 after the onset of daily administration. They were pathologically confirmed as cerebrocortical necrosis. Total thiamine levels in blood and tissues were markedly reduced at death. Blood total thiamine level decreased significantly on day 7 of amprolium administration, and reached to the level as low as that seen at death about 2 weeks before the onset of abnormal electroencephalograms. Significant decrease in a thiamine-dependent enzyme, erythrocyte transketolase activity, and increase in thiamine pyrophosphate effect were detected about 2 weeks before the onset of abnormal electroencephalograms. Pathological changes and cerebral autofluorescence observed under ultraviolet light were also examined at death.