The hippocampal GABAergic interneurons are responsible for controlling the input of large principal cell populations, and they thereby determine the oscillatory discharge patterns and synaptic plasticity in the hippocampus. Such oscillations within neuronal systems serve various complex functions, such as perception, cognition, plasticity and memory. The aim of this study is to define the function of GABAergic synaptic transmission in the dentate gyrus (DG) of the hippocampus in the different stages of inhibitory avoidance (IA) learning and memory in the rat. Two cannulae were implanted above the hippocampal DG. Then the rats were trained on a step-through IA learning task. Each rat received intra-DG injection of picrotoxin (PTX) or saline before training, after training or before the retrieval test. The results show that post-training injection of PTX impaired the IA memory. On the other hand, pre-training and pre-retrieval injection of PTX had no significant effect on the IA activity. Therefore, it seems that GABAergic transmission in the DG is involved in the consolidation step (but not in the acquisition and retrieval steps) of the IA task by controlling the input to the principal cells.