Endogenous opioid peptides modulate and regulate processes of central excitability. Furthermore, opioids are thought to interfere with processes of learning and memory storage. In order to study the effects of endogenous opioids on both processes we injected in the course of development of pentylenetetrazol kindling the opiate receptor antagonist naloxone, and tested the animals afterwards in a shuttle-box task. It was found that naloxone pretreatment had dissociative effects. There was no effect on seizure outcome, whereas the learning deficit was ameliorated in the kindled group. The data suggest that endogenous opioid peptides contribute to the learning deficit found in pentylenetetrazol-kindled rats.