An unusual type of hypertrophic astrocytes termed plump polygonal astrocytes (PPA) has been observed in the feline central nervous system which was characterized in a first preliminary study of 17 cats. These cells presented an oval to polygonal shape, measured about 20 microm in diameter, and displayed short, barely detectable processes. The condensed, hyperchromatic, eccentric nucleus was surrounded by an abundant, homogenous, eosinophilic cytoplasm. These GFAP-and S-100-positive and vimentin-negative cells were predominantly found in brains showing status spongiosus and less frequently in association with inflammation and in brains lacking histological lesions. They were mainly detected in white matter areas of the hindbrain. In addition, these cells were also observed in the dentate hilar region adjacent to degenerated neurons and a small amount of PPA were positive for caspase-3. It remains to be determined if PPA represent a specific type of reactive astrocytes and whether they are characteristic for a specific cause or response in the feline brain.