1) Cat, s hypothalamus was electrically stimulated with very thin bipolar-electrodesneedle and the water content of the cerebral cortex was measured by Hatschek's cobalt chloride method. 2) In case of simple puncture of the hypothalamus, the water content increased compared with the normal cat. But no difference was observed by changing the part of puncture. 3) By electrical stimulation of the anterior hypothalamic nucleus, ventromedial hypothalamic nucleus, dorsomedial hypothalamic nucleus and posterior hypothalamic nucleus the water content of brain increased more than in case of simple puncture, while by that of the lateral hypothalamic nucleus showed no change. 4) From the changes of pupils and respiration, the water content increased when they showed sympathetic reaction, while it did not change or slightly decreased when they showd parasympathetic reaction. 5) From the above-mentioned results, it would appear that the sympathetic system plays a more important role in the changes of the water content than the parasympathetic system.