Inclusion Criteria:

• Patients with acute ischemic stroke within 3 hours of onset, with a clearly defined time of onset.
• Patients who have been revealed to have occlusion on one side of the middle cerebral artery (M1 or M2 portion) on MRA before the start of treatment.
• Patients for whom consent has been obtained from either themselves or from their legally acceptable representatives in written form.

Exclusion Criteria:

• Patients with very light neurological symptoms (an NIHSS score of <= 4) or with rapidly improving symptoms before the start of treatment.
• Patients with serious neurological disorders (an NIHSS score of >= 23), or serious consciousness disorders (a Japan Coma Scale score of >= 100) before the start of treatment.
• Patients with functional disorders (a mRS score of >= 2) before stroke onset.
• Patients who have been administered drugs that are not allowed to be administered concomitantly with alteplase (other thrombolytic agents) after the stroke onset.
• Patients who have been revealed to have extensive early ischemic change (an Alberta Stroke Program Early CT score of <= 6) on computed tomography (CT) before treatment.
• Patients who have been revealed to have obvious occlusion in the blood vessel except for the middle cerebral artery on MRA before treatment.
• Patients who are forbidden to undergo magnetic resonance imaging (MRI).
• Patients who are defined as having cerebral hemorrhage or subarachnoid hemorrhage (SAH) on CT before treatment.
• Patients whose symptoms suggest SAH.
• Patients with hemorrhage (gastrointestinal hemorrhage, urinary hemorrhage, retroperitoneal hemorrhage, or hemoptysis).
• Patients with a platelet count below 100,000/mm3.
• Patients with fasting blood glucose levels of < 50 mg/dL or > 400 mg/dL.
• Patients whose activated partial thromboplastin time (APTT) is prolonged due to heparin administration within 48 hours before stroke onset.
• Patients who have been administered oral anticoagulants with values of the international normalized ratio of prothrombin time (PT-INR) of > 1.7.
• Patients who have a systolic blood pressure of > 185 mmHg or a diastolic blood pressure of > 110 mmHg.
• Patients who need antihypertensive therapy (e.g. continuous infusion of antihypertensive drug etc.) to lower blood pressure below those limits under the preceding article.
• Patients who have a history of intracranial hemorrhage, or who have a disease considered to increase the risk of intracranial hemorrhage such as an intracranial tumor, cerebral aneurysm, or intracranial arteriovenous malformation, etc.
• Patients who have a history of stroke within 3 months before onset.
• Patients who were operated on or injured their head or spinal cord within 3 months before onset.
• Patients who have a history of gastrointestinal or urinary tract hemorrhage within 21 days before onset.
• Patients who had a major surgery or serious trauma (except for head or spinal cord trauma) within 14 days before onset.
• Patients who have a history of organ biopsy, arterial puncture, or lumbar puncture within 10 days before onset.
• Patients with severe hepatic dysfunction or severe renal dysfunction.
• Patients with acute pancreatitis.
• Patients who had a seizure at the onset of stroke.
• Patients who have a history of hypersensitivity to protein preparations.
• Patients who are lactating, pregnant, probably pregnant, or menstruating.
• Patients with malignant tumors.
• Patients with acute myocardial infarction (AMI) or pericarditis after AMI.
• Patients with concurrent infectious endocarditis, moyamoya disease (Willis circle occlusion syndrome), aortic dissection, or neck trauma, etc.
• Patients with strong suspicion of ischemic cerebrovascular disorder caused by non-thrombotic occlusion or any other hemodynamic condition.
• Patients judged to be difficult in monitoring for 3 months by their physician.
• Patients who have participated in other clinical trials during the last 3 months.
• In addition to the above exclusion criteria, patients judged to be inadequate to participate in this study by their physician.