The dynamics of excitatory (glutamate, aspartate) and inhibitory (GABA, glycine) neurotransmitter amino acid contents in the cerebrospinal fluid were studied in 110 patients with hemispheric ischemic insult. These studies revealed significant increases in the levels of glutamate and aspartate in the first six hours of illness, and the level and duration of these changes correlated with the severity of the insult. Peak GABA and glycine levels were seen at the end of the first day after strokes, reflecting the delayed activation of the mechanisms of protective inhibition. The insufficiency of GABAergic mediation in strokes located in the hemispheres to a significant extent mirrored the severity of clinical features and the potential of restorative processes. Early significant biochemical criteria were identified for objective assessment of the severity of brain ischemia, and these had prognostic value for the course and outcome of strokes. The most unfavorable prognostic signs were the presence of low (or undetectable) GABA levels in the first days after insult and progressive increases in aspartate levels to the third day on the background of sharp reductions in glutamate levels (after initial elevation on the first day).