The purpose of this research is to: 1) perform both 3-[18F]-FACBC and [11C-methyl]-Lmethionine brain tumor PET imaging studies in patients with primary brain tumors who have previously been treated and are now suspect for having recurrence or progression of disease (a pilot study, n=20); 2) perform only 3-[18F]-FACBC PET imaging studies on an additional set of patients with primary brain tumors who have previously been treated and are now suspect for having recurrence (n=10) . 3) obtain organ/tissue and body radiation dosimetry information following i.v. injection of 3-[18F]-FACBC; 4) look for potential correlations between the scan results obtained from those patients enrolled to 03-028 and the patients' past medical treatment; The first set of 20 patients will agree to two PET studies. One study will involve the i.v.