The recognition of the significance of amino acids as mediators of chemical neurotransmission in the mammalian central nervous system has grown extensively in recent years, and no fewer than 16 of these simple compounds have been proposed to function as excitatory or inhibitory neurotransmitters in the brain (Enna, 1978a, Watkins and Evans, 1981, Toggenburger et al., 1982, Recasens et al., 1982; Iwata et al., 1982; Baba et al., 1983; Enna and Gallagher, 1983; Foster and Fagg, 1984). As the role of amino acids in neurotransmission has become apparent, the search for analytical methods to investigate the neurochemical and functional aspects of amino acids in brain and peripheral tissues has gained increasing importance.