In case of the intraperitoneal application of ammonium chloride, ammonia of the rat brain was measured by Conway's microdiffusion method, and amino acid by paperchromatography; the following results were obtained. 1) During the ammonium chloride convulsions (induced by injection of 1ml. of 10% NH(4)Cl), the ammonia and aspartic acid contents of the rat brain increased remarkably, while glutamic acid, glutamine and γ-amino butylic acid contents decreased. 2) Ammonia and amino acids were estimated in 3 hours after NH(4)Cl injeetion (1ml. of 5% NH(4)Cl), and the following data were obtained. a. Ammonia level remarkably rose five minutes after injection, and gradually returned to normal level 3 hours after. b. Glutamic acid decreased. c. The rise of glutamine level found 10 minutes to 1 hour after the application. d. γ-amino butylic acid decreased. e. Aspartic acid level rose on early period. The Conclusion is as follows: 1) In the rat brain, the free ammonia increased after NH(4)Cl injection. 2) Ammonia increased after NH(4)Cl injection was probably reduced, initially by aspartie acid synthetase system and thereafter by glutamine synthetase syestm.