Inclusion Criteria:

• Patients must have histologically confirmed diagnosis of WHO grade IV primary malignant glioma (glioblastoma multiforme or gliosarcoma). Patients will be unresectable or have multifocal disease.
• Age > or = to 18 years and a life expectancy of >12 weeks.
• Evidence of measurable primary CNS neoplasm on contrast enhanced MRI.
• An interval of at least one week between prior biopsy or four weeks from surgical resection and enrollment on this protocol.
• Karnofsky > or = to 60%.
• Hemoglobin > or = to 9g/dl, ANC > or = to 1,500 cells/microliter, platelets > or = to 125,000 cells/microliter.
• Serum creatinine ≤ 1.5 mg/dl, serum SGOT and direct bilirubin ≤ 1.5 times upper limit of normal (if the total bilirubin is greater than or equal to 1.5 x the upper limit of normal, then the direct bilirubin must be ≤ 1.5 x the upper limit of normal).
• Signed informed consent approved by the Institutional Review Board prior to patient entry.
• If sexually active, patients will take contraceptive measures for the duration of the treatments.

Exclusion Criteria:

• Pregnancy or breast feeding
• Co-medication that may interfere with study results; e.g. immuno-suppressive agents other than corticosteroids.
• Active infection requiring IV antibiotics.
• Treatment with radiotherapy or chemotherapy for a brain tumor, irrespective of the grade of the tumor.
• Evidence of > grade 1 CNS hemorrhage on baseline MRI or CT scan.

Avastin-specific Exclusion Criteria:

• Inadequately controlled hypertension (defined as systolic blood pressure > 150 and/or diastolic blood pressure > 100 mmHg on antihypertensive medications)
• Any prior history of hypertensive crisis or hypertensive encephalopathy
• New York Heart Association (NYHA) Grade II or greater congestive heart failure
• History of myocardial infarction or unstable angina within 6 months prior to study enrollment
• History of stroke or transient ischemic attack within 6 months prior to study enrollment
• Significant vascular disease (e.g., aortic aneurysm, aortic dissection)
• Symptomatic peripheral vascular disease
• Evidence of bleeding diathesis or coagulopathy
• Major surgical procedure, open biopsy, or significant traumatic injury within 28 days prior to study enrollment or anticipation of need for major surgical procedure during the course of the study
• Core biopsy or other minor surgical procedure, excluding placement of a vascular access device, within 7 days prior to study enrollment
• History of abdominal fistula, gastrointestinal perforation, or intra-abdominal abscess within 6 months prior to study enrollment
• Serious, non-healing wound, ulcer, or bone fracture
• Proteinuria at screening as demonstrated by either urine protein:creatinine (UPC) ratio > or = to 1.0 at screening OR urine dipstick for proteinuria ≥ 2+ (patients discovered to have ≥2+ proteinuria on dipstick urinalysis at baseline should undergo a 24-hour urine collection and must demonstrate ≤ 1g of protein in 24 hours to be eligible).
• Known hypersensitivity to any component of Avastin
• Pregnant (positive pregnancy test) or lactating. Use of effective means of contraception (men and women) in subjects of child-bearing potential