Purposing to get some hints on cause and early diagnosis for cerebrocortical necrosis (CCN), CCN was produced in three healthy calves by the oral administration of amprolium. All three calves showed central nervous signs characterized by ataxic gait, clonic spasm, astasia and opisthotonus, from 24 to 49 days after the start of daily administration of 321-418 mg/kg amprolium. They showed bradycardia from about 20 days before the appearance of the nervous signs, which was supposed to be a finding of primary change and to be useful for early diagnosis of CCN. At necropsy of the two calves, large necrotic lesion was found in the cerebral cortex, and tissue thiamine levels decreased significantly, especially in cerebrum and cerebellum. In the other calf, injection with 25 mg thiamine tetrahydrofurfuryl disulfide (TTFD) was proved to be effective for the recovery of clinical signs. No significant changes in thiamine level were recorded in the whole blood, but those in erythrocytes decreased slightly at about a week before the appearance of the clinical signs. No significant alteration of thiamine excretion was observed in urine. Those findings suggest that CCN in calves is caused by thiamine deficiency and that the blood thiamine levels cannot be used for diagnosis of CCN.