Effects of visual deprivation on the induction of epileptiform activity were studied in layer II/III of mature rat primary visual cortex. Field potentials were evoked by stimulation of layer IV in slices from control and dark-reared (OR) rats. Picrotoxin (PTX)-induced epileptic activity was characterized by spontaneous and evoked epileptic field potentials (EFPs). The results showed that OR slices demonstrate greater susceptibility for induction of spontaneous EFP. PTX-induced changes in the properties of evoked field potentials also showed higher tendency of OR animals to epileptogenesis. In both groups, field potentials are consisted of pEPSP₁ (population excitatory post-synaptic potential 1, i.e. first negativity) and pEPSP₂ (second negativity). PTX significantly increased the amplitude and duration of pEPSP₂, but it had no significant effect on pEPSP₁. PTX-induced changes in characteristics of pEPSP₂ were significantly higher in OR slices. It is concluded that visual deprivation causes lasting changes in layer II/III of visual cortex that retain in slices and predispose this area for PTX-induced epileptiform activity.