Effect of increase in rate of superfusion of the medium on the EPSC evoked by stimulation of Schaffer collateral was studied in CA1 pyramidal neuron of rat hippocampal slice under whole-cell voltage-clamp. Increase in superfusion rate of the medium slowly and markedly augmented the amplitude of EPSC without changing those of both AMPA-induced current and IPSC evoked by stimulation of striatum oriens. Paired pulse ratio of the EPSC decreased during the superfusion and Ca²⁺-dependence curve of the EPSC amplitude obtained by changing the [Ca²⁺]_o showed marked increase in maximum response without changing the ED₅₀ in the fast superfusion. Fast superfusion produced rightward shift of the maximum peak in the amplitude distribution histogram of the evoked EPSCs in low [Ca²⁺]_o, indicating increase in quantal size of the transmitter release. Furthermore, application of DPCPX, an antagonist for A₁ receptor, also augmented the EPSC amplitude, and the fast superfusion did not cause additional augmentation of the EPSC amplitude in the presence of DPCPX. These results suggest that major cause for the augmenting effect may be disinhibition of glutamate release from the presynaptic terminal due to increase in clearance of adenosine normaly existing nearby the synapse and inhibiting the transmitter release. [J Physiol Sci. 2007;57 Suppl:S145]