By means of the ion-exchange chromatography free amino acids and their related compounds in the fresh brain tissue have been estimated. As for the test material, pieces of the cerebral cortex sectioned at the time of the surgical operation in the patients with cerebral tumor or with epilepsy are used. As the result we have obtained the following notworthy differences when compared with the results previously reported by us concerning several species of mammalians. They are: (1) In the human brain there is a conciderable amount of cystathionine. Namely, 19.4 to 43.2mg/100g wet weight, and this substance is far smaller or not recognizable in other animals; and (2) the amounts of γ-aminobutric acid and taurine are a good deal smaller than animals. Moreover, in general the pattern of the free amino acids in the human cerebral cortex may be said to resemble closely that in dog.