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, patients who cannot get acute MRI because of contraindication to or unavailability of MRI, acute ischemic stroke of moderate severity (NIH Stroke Scale less than or equal to 16 and ischemic changes on CT scan less than approximately one third of the volume of the middle cerebral artery territory), no evidence of hemorrhage on CT, and no other clinical, radiological or laboratory features associated with increased risk of hemorrhage with thrombolytic therapy.