A variety of therapeutic maneuvers of the arteriovenous or carotidcavernous fistulas has been tried and mainly discarded as inadequate because of complicated factors such as an anatomical situation of the fistula, and embolus of predetermined size and configuration, and introducing method. The fistulas have been embolized by a variety of materials with no gain of wide acceptance. One of the major problems inherent in the procedure is the inability to control the ultimate location of the embolus, which is closely related to predetermined size and shape of the embolus. To get around this difficulty, a piece of the laminaria stalk shappen into a small columnar bar was used as an embolus in this experiment. The laminaria, sea weed used for a slow dilatation of the uterine cervical orifice in gynecological practice, has specific nature of gradual increase in its volume on contact with water or tissue fluids, expanding only in width, radial direction, but not in length. It expanded gradually with maximal increase of 3.3 times the original width by 12 hours of the contact and with increase of more than 80% of its maximal expansion by three to four hours contact. In a series of experiments, arteriovenous fistulous lesions have been created in albino rats, using a portion of jugular vein implanted on the cervical carotid artery, and it has been tried to occlude the excluded fistulous segment with the help of the laminaria stalk. A stalk of laminaria with diameter of one third of vascular lumen could easily reached to the fistulous point by the arterial pulse and thrust because the stalk was fairly smaller relative to the size of the vessel, and it occluded the lumen of the vessel near totally by a slow expansion of it into as large as the luminal size of the vessel within a couple of hours after lodging in the vessel.