The experiments were carried out on 48 rabbits weighing between 1.7 and 2kg. The occurrence and changes of experimental brain edema have been studied by calculating wet weight, volume, dry weight, and percentage of both water content and swelling in the rabbits. The brain edema and swelling were produced by expansion of laminaria which was expanded gradually in the supratentorial extradural space of rabbit, and also, the brain edema with swelling were induced by intravenous injection of distilled water and pitressin. The effect of mannitol and steroid to these experimental brain edema with swelling and, especially, the effect and reaction of ethyl alcohol and diphenyl hydantoin on brain edema in distilled-water and pitressin groups were studied and the results obtained are as follows: The weight, volume, and percentages of water content and swelling in the compressed sides of hemisphere showed higher values compared them to the opposite noncompressed hemisphere in the "laminaria-compression" group and showed gradually increasing tendency as the time elapsed. The effect of mannitolization to "laminaria-compression" group showed anti-brain edema reaction while there showed no such effect after steroid injection. The acute brain edema with swelling was demonstrated in pitressin and distilled-water group by showing increased percentages of water and swelling than those of control group. Although the intravenous dilantin injection to these experimental groups showed no appreciable effect on anti-brain edema reaction and effect.