Proceeding from estimation of the 14CO2 release from [5-14C]alpha-ketoglutarate, [1-14C] gamma-aminobutyric acid (GABA), [1,4-14C] succinate and [4-14C] aspartate (0.4-1 mM) during their incubation with homogenates of different brain areas with regard for the label position and stereospecificity of decarboxylation of citrate formed due to the metabolism, the relative intensity of their catabolism is determined: [1,4-14C] succinate much greater than [4-14C]aspartate greater than [5-14C] alpha-ketoglutarate much greater than [1-14C]GABA. The label release with catabolism of [1-14C] alpha-ketoglutarate considerably exceeds the intensity of decarboxylation of the above enumerated substrates. In all cases the maximum release of 14CO2 has been registered in the cortex homogenates, the minimum--in the medulla homogenates, and only under long-term incubation with high concentration of GABA (50 mM) maximum catabolism was registered in the medulla. Preincubation of nervous tissue with pyridoxal-5'-phosphate (40 microM) results in significant acceleration of catabolism of [1-14C] alpha-ketoglutarate, [5-14C] alpha-ketoglutarate and [4-14C] aspartate with an inconsiderable increase of catabolism of the rest of labelled substrates.