1. some of Habu-bitten patients was produced extensive myonecrosis, which left behind functional disorder. And obliterative changes was elicited in arteries passing the necrotized muscle. It is therefore considered that this extensive and severe myonecrosis would have resulted from ischemia due to the obliterative arterial lesion, which must have been produced by direct invasion of the arterial wall by Habu venom.This experiment was carried out to see whether Habu venom would effectively produce arterial lesion.2. When 2mg. per 0. 1ml. of Habu venom was injected near the femoral artery of guinea pigs, the arterial lesions were histologically observed. The results were as follows, i) adventitial and perivascular hemorrhages, exudation of blood plasmas and necrosis of tissues in the injected area, ii) swelling, -degeneration, detachment from internal elastic menbrane and loss of the endothelial cells in intima, exudations of leucocytes into subendothelial spaces, subendothelial hemorrhages, iii) development of thrombus in the arterial cavities.3. Degenerative arterial lesions as mentioned above were found till 2 or 4 days after the injection of Habu venom, and then intimal cellular thickening to be considered as regenerative change wae gradually produced in the intimal layers.4. On the basis of these finding it is evident that the necrotic and obliterative arterial lesions are primarily caused by Habu venom.