In this study the ultrastructure of motor cortex adjacent to alumina cream (AC) deposits was studied during the latent, convulsive and remission stages of an experimental model of epilepsy in cats. Findings were compared with those observed in sham-operated animals. Where AC was injected, amorphous material surrounded by macrophages containing phagocytic vacuoles was observed. At the edge of these areas, neither fibrous capsule, nor other inflammatory elements were seen. Changes in size and number of fibrous astrocytic processes and morphological signs of progressive degeneration of neuronal elements at the perilesional cortex were found through the latent, convulsive and remission stages. These findings support the idea that presence of clinical and EEG seizures in AC lesioned animals is independent of scar formation and other inflammatory elements. On the other hand, the significance of increased astrocytic processes and progressive degeneration signs of the perilesional cortex in the physiopathogenesis of convulsive activity requires further investigation. (Arch. Invest. Méd. (Méx) 7:157, 1976).