The mossy-fibre axons of the hippocampus form a dense plexus, uniquely rich in chelatable zinc. Because the metal is apparently concentrated within the terminal bags of the axons, it has been hypothesized that the zinc is involved in mossy-fibre synaptic transmission. Although some electrophysiological findings have favoured the hypothesis, neither preferential uptake of zinc into the hippocampus nor depolarization-induced release of zinc from hippocampal tissue has previously been found. Using the hippocampal slice preparation, we now report that the mossy-fibre neuropil and cells of origin (dentate granule cells) take up zinc preferentially, and that electrical stimulation selectively facilitates both uptake of exogenous zinc into mossy-fibre neuropil and release of previously incorporated 65Zn from the tissue. The results suggest that the role of zinc in mossy-fibre axons is dynamically linked to neural signalling processes.