The effects of monosodium glutamate (MSG) on the activities if tyrosine hydroxylase (TH), dopamine ${eta}$-hydroxylase (DBH), tryptophan hydroxylase (TPH) and monoamine oxidase (MAO) in various regions (cerebral cortex, striatum, midbrain, pons and medulla of nat brain have been determined. It was observed that up to 1mM MSGhad no significant effects on the activities of brain tyrosine hydroxylase, dopamine ${eta}$-hydroxylase, tryptophan hydroxylase and monoamine oxidase in all regions of rat brain. These results indicated that MSG itself exerted no direct effect on the important enzymes synthsizing and metabolizing the monoaminergic neuronal system.