Recent in vivo NMR studies of the brain have identified important metabolites and have measured their flows in animals and humans. 13C labeled molecules have been particularly important for these studies because the low 13C natural abundance allows labeled metabolites to stand out in NMR spectra. Flows of labeled glucose into the glutamate, glutamine and GABA cerebral pools, measured by 13C NMR, establish the rate of glucose oxidation. In the same experiment, the rates of glutamate and GABA neurotransmitter release and recycling can be measured. Methods for performing these experiments and for interpreting the signals are described in this book, which provides the first integrated account of this rapidly growing field of functional, cerebral metabolism.