A Dose Escalation and Safety Study of Plasmin (Human) In Acute Lower Extremity Native Artery or Bypass Graft Occlusion

Inclusion Criteria: * Age ≥ 18 years. * Women of childbearing potential must use adequate contraception for the duration of the study and must have a negative pregnancy test prior to study entry. * Unilateral limb ischemia: SVS acute ischemia Category I or IIa. * Onset of symptoms \</= 14 days. * Thrombosed (non-embolic) infrainguinal graft (synthetic, autologous, or single outflow composite) or infrainguinal native artery. For native arteries, only occlusions of ≥ 10 cm in length are eligible. * Diagnosis of occlusive thrombus in the graft or artery by arteriography after Informed Consent is obtained. * Ability to traverse the thrombus with a guidewire. * Signed informed consent prior to study entry. Exclusion Criteria: * Clinical evidence of significant disease that may interfere with the patient successfully completing the trial. * Women who are pregnant or lactating, or first 10 days post-partum. * Previous hemorrhagic stroke at any time. Thrombotic or embolic stroke or cerebrovascular events (including transient ischemic attack (TIA)) within one year. * Intracranial or spinal neuro-surgery, or severe intracranial trauma in the last 3 months. Major surgery, organ biopsy, or major trauma within the last 10 days. Lumbar puncture or non-compressible arterial puncture in the last 10 days. Intra-ocular surgery within the last 10 days. * Current bleeding diathesis. Active gastrointestinal or organ bleeding. Minor bleeding such as normal menses, cystitis, or minor hemorrhoidal bleeding are not exclusions. * Uncontrolled arterial hypertension, defined as a systolic blood pressure \> 180 mmHg or diastolic blood pressure \> 110 mmHg. * Known intracranial neoplasm, aneurysm, or arterio-venous malformation. * Platelet count \< 75 x 10e9/L. * Occlusion of a graft within 6 months of placement. * Medically unable to tolerate an open vascular procedure. * Known prothrombotic condition. * Hemoglobin \<10.0 g/dL * Impaired renal function or renal disease that constitutes a contraindication to contrast angiography, including creatinine \> 2.0 mg/dL or subjects on renal dialysis. * Treatment with a glycoprotein IIb/IIIa class of platelet inhibitor within the past 5 days, for example, abciximab (ReoPro®), eptifibatide (Integrilin®) or tirofiban (Aggrastat®). * Treatment with warfarin (Coumadin®) and with an INR of \>1.7 (elevated INR at screening may be corrected prior to study enrollment.)