The Stealth dilation catheter was introduced for the intravascular treatment of two patients with acute and unstable ischemic stroke due to hemodynamically significant stenosis in the one case of the middle cerebral artery and in the other of the vertebral artery. Cerebral perfusion study on the two cases showed a moderately low flow area in the right cerebral hemisphere and in the left cerebellar hemisphere, respectively. Percutaneous transluminal angioplasty (PTA) using the Stealth catheter was conducted. The two cases showed marked improvement in their neurologic state just after PTA with marked increase in cerebral perfusion in the relevant regions.