Abstract: Wister newborn male rats were divided into two groups, one group was administrated MSG(4g/kg)by s.c. every two days from the second day to the tenth after birth. Another group was gaven N.S. as control. At the hundredth day, the rats were decapitated. We found that the rats' body weight and length in experimental grounp reduced significantly as compared with those in control group. There was no difference between two groups on brain weight and intelligence, although the reduction of weight of viscera was obvious in experimental group. The nucleus arcuatus were apparently smaller and the number of neurone were obviously less than those in the control. The weights of piutitary glands in experimental group were as 55.8 per cent as those in control group. The result of immunohistochemistry revealed the presence of GH-secreting cell in the pituitary glands of rats treated with MSG, but the number and area of these cells measured by image analyser were smaller. According to these results, we consider that the damage of nucleus arcuatus induced by MSG obviously decreases the secretion of growth hormon releasing factor, therefore, the secretion of GH is insufficant in pituitary gland and the differentiation of GH-secreting cells can not be promoted. The conc- lusion is that the dwarfism model induced by MSG in rats is very similar to pituitary dwarf of human being,

Key words: monoscdium glutamate, pituitary dwarf, arcuate nuclei, pituitary, immunohistochemisry