Study Population: Patients will be selected by criteria to minimize likelihood of toxicity and maximize likelihood of response. These criteria include age 18-80 years old, acute ischemic stroke of moderate severity (NIH Stroke Scale less than or equal to 16 and lesion volume on diffusion MRI less than approximately one third of the volume of the middle cerebral artery territory), positive MRI evidence of hypoperfusion corresponding to the acute stroke symptoms, no MRI evidence of chronic micro-hemorrhages, and no other clinical, radiological or laboratory features associated with risk of hemorrhage with thrombolytic therapy.