Dilantin had been shown to reduce the post-tetanic potentiation (PTP). The aim of the present study was to study the role of the PTP in the long-term memory. Dilantin in a dose of 16 and 32 mg/kg did not effect the realization of defensive reflexes to a conditioned stimulus (CS, light flashes) in alert non-immobilized rabbits. A week disinhibition of movements in response to the combination of the light flashes with continuous illumination (conditioned inhibition, CI) took place. Similarity of responses to CS and its combined action with the pain reinforcement did not change in most of the neurons under study and was enhanced in some of them. Distinction between responses of most neurons to CS and CI did not disappear but in some of them became less expressed. The data obtained imply that PTP does not play a decisive role in the long-term memory storage.