During central nervous system (CNS) development, intermediate filaments are subjected to a sequential remodelling process. Nestin is a distinct intermediate filament which is transiently expressed in proliferating neuroepithelial stem cells during the neurulation stage of development. Nestin re-expression in the adult rat was studied following transient (2 h) middle cerebral artery occlusion. Seven days after the ischemic insult, nestin reactive astrocytes were found in the border zone surrounding cerebral infarction. Nestin immunoreactivity delineated a zone between infarction and the surrounding intact cerebral parenchyma. In situ hybridization for nestin mRNA showed early changes in small cells in the surround of the ischemic lesion. These results with nestin, along with other stem cell markers expressed by reactive astrocytes, suggest an embryonic reversion of the mature cytoskeleton as a response of astrocytes to cerebral injury.