The effects of glycine (Gly) and γ-aminobutyric acid (GABA) on the neurons acutely dissociated from rat visual cortex (VC) were investigated in the whole-cell mode using a conventional patch-clamp technique. GABA and Gly evoked Cl − currents (I Cl) in a concentration-dependent manner at a holding potential (V H) of −50 mV. The half maximum effective concentrations (EC 50) were 4.64 × 10 −6 M for GABA and 6.67 × 10 −5 M for Gly. Strychnine and bicuculline reversively inhibited both 10 −5 M GABA -and 10 −4 M Gly-induced I Cl in a concentration-dependent manner. The half maximum inhibitory concentrations (IC 50) of strychnine on GABA- and Gly-induced currents were 4.00 × 10 −6 M and 8.26 × 10 −8 M, respectively. The IC 50 values of bicuculline on GABA and Gly responses were 1.18 × 10 −6 M and 2.97 × 10 −4 , respectively. GABA at 10 −5 M, which is near the EC 50 of the GABA response, induced I Cl in all neurons tested n = 83). However, Gly of 10 −4 M, which is near the the Gly response, induced I Cl in 34 out of 83 neurons tested (41%). Moreover, the maximum amplitude of the Gly response was about 60% of that of the GABA response. On the other hand, the enhancement of N-methyl- d-aspartate (NMDA, 3 × 10 −4M ) response by Gly (10 −6 M) was observed in all neurons (n=36) whether they had the Gly-induced I Cl or not. In conclusion, it was proved that the VC neurons of immature rat could be classified into two classes, i.e. Gly sensitive and Gly insensitive in respect to activation of Cl − channels. There were no significant correlations between the Gly response and the facilitatory action of Gly on the NMDA response, nor between the Gly and GABA responses. The GABA response was closely correlated to the NMDA response, having a correlation coefficient of 0.86.