Amino acids are involved in many metabolic processes and in protein synthesis. In the central nervous system, they also function as neurotransmitters or neuromodulators (Davidson, 1976; Corradetti et al., 1983; Fonnum, 1981, 1984). Numerous studies have demonstrated the excitatory effects of aspartate and glutamate (Watkins and Evans, 1981); the inhibitory effects of glytine, γ–aminobutyric acid (GABA), and taurine (Schaffer et al., 1981; Lloyd et al., 1983; Roberts, 1984), and the precursor roles of tryptophan in serotonin synthesis and of tyrosine and phenylalanine in the biosyntheses of catecholamines (Sved, 1983). It is not surprising, therefore, to see an ever-increasing interest in amino acid analysis in biological samples.