This study was undertaken to determine pathological changes ol cerebrocortical necrosis (CCN) experimentally induced by given amprolium in lambs. Six healthy lambs, aging between 7 and 9 months and weighting between 11 and 15 kg were used as a material. Six lambs were divided into two groups to be three animals in each group ( group l,ll). Amprolium ( 600 mg/kg/day) was given per oral to the both groups of lambs by stomach tube during experiment. The symptoms of CCN in iambs were observed between 29 and 63 days of the experiment While the lambs in the group II were treated with thiamine ( 500 mg /day) after clinical symptoms of CCN were appeared, the lambs in the group I were not applied any treatment. Plasma tiamin concentration decreased dramatically from 4.42 µg/ml to 0 62 µg/ml (p< 0 01) and aftering treatment, inclined to 3.2 µg/ml in the lambs of group li Serum CPK, ALT, AST ve glucose concentration increased dramatically (p<0 01) The lambs in the group I were necropsied when the all symptoms ol CCN were observed. The lambs in the group II were necropsied when the clinical symptoms of CCN were disappered after treatment. At the necropsy, meningial hiperemia, swollen and oedematus brain tissues were observed in all the lambs ol group I. The slight oedema in the brain was detected in the lambs group II. Histologically, ichemic neuronal changes, perivasculer and perineuronal oedema, focal necrosis in cerebellar cortex and colliculus were determined in all the lambs of group I. The results of this research work showed that using long term and high dose of amprolium in lamb caused cerebrocortical necrosis and deficies thiamin of lambs with thiamin treatment would be of benefit in the care of CCN.