By means of ion exchange column chromatography the author carried out quantitative analyses of 14 kinds of free amino acids including the related compounds using the brain of the person who died of acute loss of blood. The parts of the brain used for the analysis were frontal cortex, corpus callosum, caudate nucleus, globus pallidus, thalamus, hypothalamus and medulla oblongata. The results are as follows. 1. In corpus callosum which contains little cellular components extremely minute quantities of phosphoethanolamine, aspartic acid, glutamic acid and γ-aminobutyric acid could be detected. 2. In globus pallidus a surprisingly large quantity of γ-aminobutyric acid could be found and it was far greater than that contained in hypothalamus. 3. In medulla oblongata only small quantities of phosphoethanolamine, aspartic acid, and glutamic acid could be detected. Likewise γ-aminobutyric acid was found not so abundant. This seems to be due to the fact that the present experiment was conducted with medulla oblongata including white matter. 4. Although only in a small quantity, cystathionine could be assayed in all these parts except globus pallidus and thalamus. 5. Even from the comparative biochemistry the present quantitative analyses gave an interesting contrast to the values obtainable in the brains of lower animals. 6. Although it was difficult to recognize any distinct difference in the pattern of amino acids between the adult brain and the infant brain, there was a clear-cut difference in the amino acid pattern of the adult brain and that of the fetal brain. Namely, in the adult human brain there exist far greater quantities of aspartic acid, glutamic acid, γ-aminobutyrie acid, and N-acetylaspartic acid than those in the fetal brain and conversely far less quantities of phosphoethanolamine and taurine than in the latter. Likewise tyrosine detected in the fetal brain could not be recognized in the adult human brain.