Sox-2 is a transcription factor that is expressed by self-renewing and multipotent stem cells of the embryonic neuroepithelium. Very little is however known about Sox-2 expression in the adult brain and therefore we used immunohistochemistry to examine its distribution and co-localization with specific cell markers. We found that Sox-2 was expressed by actively dividing neural progenitor cells in the neurogenic regions in the adult rat brain, the subventricular zone of the forebrain and the subgranular zone of the dentate gyrus in the hippocampus. Cells expressing immature neuronal markers were essentially Sox-2 immunonegative. Sox-2 was also found to be expressed by glial fibrillary acidic protein immunopositive astroglia, widely distributed in the brain parenchyma. Given the fact that several studies have established the neurogenic capacity of a specialized type of astroglia in the adult brain, the findings of Sox-2 expression in parenchymal astroglia are of potential interest. We conclude that Sox-2 might, in combination with appropriate cell-specific markers, constitute a useful marker to study the in vivo dynamics of the neural progenitor cell compartment also in the adult brain.