Inclusion Criteria:

• Symptoms of acute ischemic stroke; acute ischemic stroke is defined as the sudden onset of a measurable neurological deficit presumably attributable to focal cerebral ischemia, and otherwise not attributable to ICH or other disease process
• Symptom onset within 0-6 hours of administration of study medication Stroke onset is defined as the time of first symptoms or signs of neurologic deficit. If the onset of symptoms/signs is unwitnessed, time of onset is presumed to be the last time the patient was observed to be intact
• Neurologic deficit on examination with NIHSS of greater than 4 and less than 23
• In women of childbearing potential, a negative urine pregnancy test prior to enrollment (to be confirmed later by serum test)
• Signed informed consent by subject or authorized representative

Exclusion Criteria:

• Computed tomography scan of the brain with evidence of intracranial hemorrhage or any finding not consistent with acute ischemic stroke as cause of presenting symptoms
• CT imaging demonstrating hypodensity more than 1/3 of MCA territory or mass effect
• Neurological (other than presenting stroke) or psychiatric condition that may affect the patient's functional status or that may interfere with the patient's assessment
• Clinically relevant pre-existing neurological deficit (historical modified Rankin score greater than 2 regardless of cause)
• Treatment with tissue plasminogen activator or other thrombolytic agent within 3 months, including treatment with tissue plasminogen activator for current stroke
• Need for treatment with anti-platelet agent or anticoagulant within 36 hours
• Previous stroke or serious head trauma within 3 months
• Major surgery within previous 14 days
• History of intracranial hemorrhage
• Rapidly improving or minor symptoms
• Symptoms suggestive of subarachnoid hemorrhage
• Gastrointestinal hemorrhage or urinary tract hemorrhage within previous 21 days
• Arterial puncture at noncompressible site within the previous 7 days
• Seizure at onset of stroke
• Use of oral anticoagulant medications at time of symptom onset or treatment with subcutaneous or intravenous heparin within previous 48 hours with elevated partial thromboplastin time
• INR values greater than 1.5
• Platelet count less than 100,000/μL
• Glucose concentration less than 40 mg/dL or greater than 400mg/dL
• Participation in another clinical trial within the last 30 days, or planned participation in another clinical trial
• Women who are currently breast-feeding
• Known resistance to activated Protein C (Factor V Leiden mutation)