The mitogen-activated protein kinase (MAPK) cascade that leads to the activation of extracellular signal-regulated kinases-1 and -2 (ERK1 and ERK2) has a key role in the differentiation of some cell types and the proliferation of others. However, several recent reports implicate this cascade in the control of synaptic plasticity in the adult brain. ERK signalling seems to be essential for characterized neuronal transcriptional events, and might also regulate synaptic targets to control plasticity. Another recently emerging story is the involvement of a 'parallel' but distinct kinase cascade leading to the activation of p38 MAPK, which might control distinct forms of synaptic plasticity.