Stimulation of the white matter between the cerebellar cortex and the deep cerebellar nuclei in rat cerebellar slices, evoked inhibitory postsynaptic potentials (IPSPs) in deep nuclear neurones. These IPSPs had reversal potentials close to –75 mV and were blocked by picrotoxinin. Stable IPSPs were evoked when the white matter was stimulated at 0.033 Hz; however, at frequencies > 0.2 Hz, the synaptic transient was suppressed. Paired-pulse depression of the IPSP occurred at inter-pulse intervals of 100–400 ms. Subsequent to stimulation at 0.2–5 Hz, a short-term depression of the IPSP occurred while a tetanic stimulation at 100 Hz caused a long-term depression. These results indicate that IPSPs in the deep cerebellar nuclei undergo activity-mediated plasticity.