administration of fluorine-18 labeled amino acid analogue, 3-fluoro-aminocyclobutane carboxylic acid (3-[18F]-FACBC) with one brain scan and one body scan only. The 3-[18F]-FACBC PET studies (n=30) will be performed under the Radioactive Drug Research Committee (RDRC) guidelines as defined and established by the Federal Drug Administration (FDA). [11C-methyl]-L-methionine is in the hospital formulary and is approved for imaging brain tumors at MSKCC. Our hypotheses include: 1) [18F]-FACBC has equal or better brain tumor imaging characteristics compared to [11C]-methionine; 2) [18F]-FACBC is not metabolized, and radiolabeled metabolites will not confound the interpretation of the images as can be the case with [11C]-methionine; 3) imaging recurrent brain tumors with [18F]-FACBC will be enhanced by lower brain (background) activity as compared to corresponding [11C]- methionine images; 4) the biodistribution of [18F]-FACBC and radiation dosimetry following i.v. administration of a 370 MBq (10 mCi) dose is safe and within FDA guidelines; 5) a 370 MBq (10 mCi) dose of [18F]-FACBC is sufficient for imaging brain tumors in a clinical setting; 6) the accumulation of [18F]-FACBC will correlate with the patients response to prior treatment and will provide prognostic information with respect to tumor progression and survival.