Orthodromically evoked field potentials were recorded in the CA1 region of hippocampal slices while perfusing the slices with media containing lead acetate. High-frequency stimulation (HFS) was applied to the stratum radiatum during lead perfusion. In half of the slices investigated, HFS resulted in an initial increase of the evoked responses which decayed again after about 10 min. In the other half the evoked responses increased only after the washout of lead and this potentiation was comparable to untreated controls. The lead-induced depression of the long-term potentiation might be related to the behavioral deficits observed in chronically lead-exposed mammals.