It has been demonstrated that neonatal administration of monosodium glutamate (MSG) results in a clearly defined lesion of the arcuate nucleus (AN) of the hypothalamus.The present study shows that fat was accumulated in the abdomen of male rats treated with MSG; weights of the body, pituitary and testis were lower, 6-EP content in hypothalamus decreased while L-EnK content increased, serum LH, FSH, TSH, GH and TS levels all decreased in varying degrees while serum PRL level significantly increased. The cAMP content lowered in pituitary, but nor in testes; clear histological changes occurred in testicular tissue; Se-GSH-Px activity in both testis and adrenal gland lowered while LPO level significantly increased. Both Se-GSH-Px activity and LPO level in liver increased.These results indicate that MSG is harmful to the function of the hypothalamus-pituitarytarget system of neonatal rats It has been demonstrated that neonatal administration of monosodium glutamate (MSG) results in clearly defined lesion of the arcuate nucleus (AN) of the hypothalamus. The present study shows that fat was accumulated in the abdomen of male rats treated with MSG; the body, pituitary and testis were lower, 6-EP content in hypothalamus decreased while L-EnK content increased, serum LH, FSH, TSH, GH and TS levels all decreased in varying degrees while serum Pituitary, but nor in testes; clear histological changes occurred in testicular tissue; Se-GSH-Px activity in both testis and adrenal gland lowered while LPO level significantly increased. Both Se-GSH-Px activity and LPO level in liver increased. results indicate that MSG is harmful to the function of the hypothalamus-pituitarytarget system of neonatal rats