There is a general agreement on the Nestin re-expression in reactive astrocytes, but its modalities differ among experimental animal species and between the latter and human material. In a series of 40 surgical specimens, including gliomas, vascular malformations, abscesses and angiomas, the glial reaction has been studied by immunohistochemistry and immunofluorescence of Nestin, GFAP and Vimentin. The observations made by immunohistochemistry were comparable with those by immunofluorescence. In some lesions, glial reaction was long-lasting and astrocytes were in the same late maturation stage. In other lesions, such as invading malignant gliomas, astrocytes occurred in different maturation stages. In comparison with GFAP, Nestin was poorly expressed in mature astrocytes and more expressed in developing reactive astrocytes, mainly in the cytoplasms, with a great variability, and much less in the processes. In the invading tumor, developing positive astrocytes were hardly distinguishable from tumor invading astrocytes that, interestingly, were much more Nestin- than GFAP-positive. In the deep tumor reactive astrocytes were no more visible. The interpretation of the findings was based on what is known on the reciprocal behavior of the three antigens in maturing astrocytes during embryogenesis and on the hypothesis of an embryonic regression of reactive astrocytes. The impossibility to distinguish them from tumor cells in the deep tumor legitimates the suspicion of their recruitment among tumor cells.