A long-lasting potentiation of synaptic transmission can be induced in the hippocampus by high-frequency stimulation of the afferent fibres1,2. This process has been regarded as a possible physiological substrate for long-term memory. From theoretical considerations on memory function it has been proposed that synaptic strengthening occurs as a result of simultaneous pre- and postsynaptic activation3, a principle which has been used in several theoretical models (for references see refs 4, 5). It thus seems important to study factors which control hippocampal long-lasting potentiation and, in particular, whether these factors act pre- or postsynaptically. A presynaptic control of long-lasting potentiation was established in experiments where two separate inputs to the same population of CA1 pyramidal cells were used6,7. Studies on the granule cell population of area dentata however, revealed, a heterosynaptic modulation of the generation of potentiation, suggesting a possible postsynaptic control also8,9. We have now studied long-lasting potentiation in the hippocampal slice preparation (CA1 region) in conditions where postsynaptic inhibition was reduced by application of γ-aminobutyric acid (GABA) receptor blockers. We found that in addition to their direct effect on inhibition, GABA blockers dramatically facilitated the induction of long-lasting potentiation. The results indicate involvement of postsynaptic mechanisms in the generation of long-lasting potentiation.