Evoked epileptiform activity (Stim. site: Schaffer Coll., SC) was monitored in adult rat hippocampal slices (n=19) using a fast optical recording system with low spatial resolution (135x135mm ²/diode) and the voltage sensitive fluorescence dye RH795. Following control stimulation (1/3min) slices were exposed to either Bicuculline Methochloride (Bic., 25mM) or to 4-Aminopyridine (4-AP, 50mM) for at least 45min. Single stimuli to SC evoked in both models a fast early depolarization which spread along known pathways in CA1, invading slightly larger areas than under control conditions. The early component increased with stim. intensity. Backpropagation to CA3 was sometimes observed in the Bic. model. Under Bic., a slow depolarization propagated along the same pathways, it lasted up to 600ms. With 4-AP a slow longlasting (up to 1s) depolarization was generated near the stim. site, it spread to the distal apical dendrites along CA1-CA3, crossed the dentate fissure and invaded the inner blade of the Dentate Gyrus; its amplitude was independent of stim. strength. This slow and longlasting component rarely invaded Str. Pyramidale and Str. Oriens. A comparable spread was not observed under Bic. treatment. The mechanisms underlying generation and spread of this late component are not yet known. It is hypothesized that glial mechanisms, related to K+ buffering, play a dominant role.