The author measured quantitatively glutamic acid, glutamine and γ-aminobutyric acid in the rat brain homogenate by paperchromatography, and obtained the following results. 1) When the brain homogenate of normal rat is incubated at 38℃ for 60 minutes under anaerobic conditions, the quantity of glutamic acid decreases slightly while the quantities of glutamic acid and γ-aminobutyric acid increase. When glutamic acid is loaded to the brain homogenate as substrate, the glutamic acid so loaded decreases markedly whereas γ-aminobutyric acid increases markedly. 2) In the case of the homogenate subjected to repeated electro-shocks, such increase in γ-aminobutyric acid is lessened. 3) In the case which received repeated insulin shocks, the increase in γ-aminobutyric acid likewise tends to be reduced. 4) These facts seem to indicate that the glutamic decarboxylase acitivity in the brain in the cases (2 and 3) mentioned above might have been slackened.