Changes in amplitudes of evoked inhibitory postsynaptic currents (eIPSCs) from rat cultured hippocampal neurons were studied using whole-cell patch-clamp technique in postsynaptic neuron and local extracellular electrical paired pulse stimulation of single presynaptic axon. Paired pulse depression (PPD) and paired pulse facilitation (PPF) were observed in studied 43 neurons. According to coefficient of variance (CV) analysis was found that CV of second respond was significantly larger than CV first by 57 % (n = 26) during depression and significanty smaller by 27 % (n = 17) during facilitation. Thus, only presynaptic mechanism underlies shortterm depression and facilitation. We also estimated quantal parameters assuming that transmitter release is reasonably described by a binomial distribution. We found that under our experimental conditions there were no significant changes in GABA release probability during PPD and PPF. The values of mean quantal content and mean number of sites of transmitter release were the same for first stimulus in pair and were equal 9.7 in depression and 5 in facilitation of synaptic transmission. The values both of them for second stimulus were significant decreased by 28 and 26% during PPD and were significant increased by 14 and 11% during PPF, respectively. Thus, there is significant difference in quantal parameters characterizing GABA release during short-term depression and facilitation of synaptic transmission.