During the brain maturation a critical period is detectable when the sensitivity of the neocortex is high. Enhanced excitatory activity is characteristic at that time while the inhibitory processes are underdeveloped. The goal of this study was to determine the effectiveness of different types of excitatory amino acid antagonists reducing the electrically evoked excitatory synaptic responses of the somatosensory cortex. Effects of the specific competitive N-methyl-D-aspartate (NMDA) antagonist 4-amino-phosphono-valerate (APV), and the specific non-competitive, non-NMDA antagonist 1-(4-aminophenyl)-3-methylcarbamoyl-7,8-methylenedioxy-5H-2,3-benz odiazepine (GYKI 53655) were analysed on neocortex slices prepared from 2-week-old and adult rats. APV caused a partial inhibition of the electrically evoked response more effectively in young animals than in adults, while the effective IC50 values were similar. In contrast, the non-NMDA antagonist had a similar effect on the slices of both age-groups.