During the last decade, the aberrant expression of normal testicular proteins in neoplastically transformed cells became common knowledge. Cancer/testis-antigens (CTAs) represent a novel family of immunogenic proteins. The MAGE genes were initially analyzed from melanomas and turned out to have an almost exclusively neoplasm-specific expression pattern. This expression pattern might contribute to the genetic instability of neoplastically transformed cells. In normal adult tissues, most 23 human MAGE genes are expressed only in the testis, but only in the mitotic spermatogonia (germ cells) and in the primary spermatocytes. The immunocytochemistry was carried out on routine, formalin-fixed, paraffin-wax-embedded 3 to 4 mm thick astrocytoma (ASTR) tissue sections. A four step, indirect, biotin-streptavidin based method was employed with alkaline phosphatase enzyme conjugation. Immunocytochemical presence and cellular localization of the MAGE-1 CT-antigen, employing anti-MAGE-1 MoAB was observed only in anaplastic, high-grade ASTRs (100%), certainly including glioblastomas, in this study. The immunoreactivity was always heterogeneous, showing a cytoplasmic pattern and loosely grouped cells with similar staining characteristics being detected within the cellular and hormonal microenvironment of the ASTRs. We never identified MAGE-1, CT-antigen expression in the lowest grade, pilocytic ASTRs. The MAGE-1 CTA expression levels may also be used to evaluate the malignant and dedifferentiation tendencies of low-grade ASTRs and predict the likelihood of mutations of the genome and further dedifferentiation towards even more malignant anaplastic ASTR and glioblastoma multiforme IPs.