AbstractThe contents of alanine, aspartate, GABA, glutamate, glutamine, glycine, serine, and lactic acid were measured in the cerebral hemispheres, midbrain, cerebellum, and pons‐medulla of rats killed by immersion into liquid nitrogen or by decapitation. The head of each decapitated rat was frozen as described. Only in the cases of lactic acid, alanine and GABA were marked post‐mortem changes observed within a few minutes after death. In rats killed 7 and 15 min after an intraperitoneal injection of (U−14C) glucose, there was a post‐mortem increae in the specific activity of GABA relative to glutamate. These post‐mortem changes in GABA support the idea that of the carbon units oxidized via the tricarboxylic acid cycle approximately 10% pass through the GABA bypath. These data are also consistent with the view that multiple pools of both glutamate and GABA exist in bra