Learning is the modification of behaviour by experience, and memory is the retention of such modifications. Since learning events might be of short duration, selective neuronal mechanisms must exist to translate transient activity into long-lasting memory. Because metabotropic glutamate (mGlu) receptors are coupled to various second messenger cascades they are ideal candidates for such translations. Their involvement in synaptic plasticity has been demonstrated recently, an important finding given that changes in synaptic efficacy are widely believed to be the physical substrate for information storage. Behavioural investigations using selective drugs have demonstrated that memory formation, especially of hippocampus-dependent tasks, is blocked by pre-training treatment with both mGlu-receptor agonists and antagonists. In contrast, agonists administered post-training might amplify memory formation. The hypothesis put forward here suggests that the primary function of mGlu receptors is to set the signal-to-noise ratio and thereby filter out unimportant or amplify important information.