Inclusion Criteria:

- Adult patients (n = 20) with primary brain tumors will be studied.

- All patients will have had previous radiation and may or may not have had
chemotherapy for treatment of the primary brain tumor.

- All patients must have either radiological or established histological diagnosis of
the following general categories: glioma (grade 2 to grade 4) previously treated with
radiation therapy and possibly chemotherapy. It is expected that some of the patients
may need a biopsy or neurosurgical procedure for diagnostic and/or therapeutic
purposes as necessary treatment of their disease. In those instances the pathologic
results will be used for correlation with the imaging findings. Only clinically
indicated biopsy and/or surgery will be done and surgery is incidental to inclusion
in the protocol.

- Patients must be 18 years or older for inclusion in this study.

- After entry into the study, the initial 12 patients are expected to be followed for
at least 1 month after the infusion of [F-18]FLT.

- The patient, if female, must be postmenopausal for a minimum of one year or
surgically sterile, or on one of the following methods of birth control for a minimum
of one month prior to entry into this study: IUD, oral contraceptives, Depo-Provera
or Norplant. These criteria can be waived at the discretion of the investigator if
the patient's intracranial tumor is considered life threatening and the one month
wait required is not in the best interest of the patient. Negative pregnancy test is
accepted.

- Pre-treatment laboratory tests for patients receiving [F-18]FLT must be performed
within 14 days prior to study entry. These must no greater or less than 4X the normal
upper or lower limits. These will include liver enzymes (SGOT, SGPT, ALK Phos, GGT,
LDH), bilirubin (direct and total), amylase, serum electrolytes, CBC with platelets
and absolute neutrophil counts, prothrombin time, partial thromboplastin time, BUN,
creatinine, and urinalysis.

- Pre-treatment radiological scans/studies (Gd- enhanced MRI and FDG-PET) for patients
receiving [F-18]FLT must be performed within 10 days of study entry.

Exclusion Criteria:

- Patients with clinically significant signs of uncal herniation, such as acute
pupillary enlargement, rapidly developing motor changes (over hours), or rapidly
decreasing level of consciousness, are not eligible.

- Patients with known allergic or hypersensitivity reactions to previously administered
radiopharmaceuticals. Patients with significant drug or other allergies or autoimmune
diseases may be enrolled at the Investigator's discretion.

- Patients who are pregnant or lactating or who suspect they might be pregnant.

- Adult patients who require monitored anesthesia for PET scanning.

- HIV positive patients due to the previous toxicity noted with FLT in this patient
group.