Structural changes in neurons and measures of oxidative stress were studied in the hippocampus of rats tolerant (ST) and sensitive (SS) to developing clonic-tonic seizures in conditions of pentylenetetrazol kindling. Sequences of 11 injections of pentylenetetrazol significantly decreased the number of normal neurons in hippocampal field CA1 in SS rats, this effect being seen in both hippocampal field CA1 and the dentate fascia in ST rats. Decreases in the numbers of normal neurons were accompanied by increases in the numbers of damaged cells in field CA4 in rats of both groups. After 21 injections, decreases in the numbers of normal neurons were seen in field CA1 in both SS and ST rats, while the numbers of damaged neurons were significantly greater than control only in ST rats in fields CA1 and CA4. The glutathione level was significantly lower in the hippocampus in both groups of rats than in controls. Thus, rats " tolerant" to developing convulsions show signs of oxidative stress and neurodegenerative changes in the hippocampus. This suggests that oxidative neuron damage leading to neurodegeneration in the pentylenetetrazol kindling model is not directly associated with convulsive activity.