We describe a simple method, using readily available minaturised components, for inducing and monitoring long-term potentiation (LTP) at perforant path-granule cell synapses in the dentate gyrus of the freely moving mouse. Tetanic stimulation induced LTP of the field EPSP and the population spike which persisted for more than 24 h but was not present 10 days after the tetanus. The potentiation of the population spike was proportionately greater than the potentiation of the EPSP (E-S potentiation). Induction of LTP was blocked by intraperitoneal injections of the N-methyl-D-aspartate (NMDA) receptor antagonist, 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP).