The cellular changes in the neighbourhood of an alumina cream epileptogenic focus and in the mirror focus in chronic experiments in cats have been studied. According to the neuroglial morphology, four layers are described around the alumina cream lesion. At an ultrastructural level, and increase in gap junctions with a great amount of gliofilaments in astroglial processes are observed. There is a decrease in the number of neurons in the vicinity of the alumina cream. Some are coated by glial processes filled with gliofilaments. The dendrites of the pyramidal neurons in the mirror focus show long mitochondria. The possible significance of these data, in relation with the current theories about epileptogenicity, are discussed.