By screening a human testis cDNA library with glioma patients' sera, we isolated a transcriptional factor, SOX6. Here, we analyzed SOX6 expression in gliomas having a range of malignancy grades using immunostaining. Murine Sox6 is a transcriptional factor that is specifically expressed in the developing central nervous system and in the early stages of chondrogenesis in mouse embryos. The reverse transcription-polymerase chain reaction (RT-PCR) revealed that the SOX6 gene was more highly expressed in glioma tissues and fetal brain than in normal adult brain and other cancer cells, except melanoma cells. Immunohistochemical analysis with the anti-SOX6 antibody showed that all the glioma tissues analyzed (14 glioblastomas, 14 anaplastic astrocytomas, 3 anaplastic oligoastrocytomas, 5 diffuse astrocytomas, 1 oligodendroglioma, and 1 pilocytic astrocytoma) expressed SOX6 in tumor cells, but only a few SOX6-positive cells were detected in nonneoplastic tissues from the cerebral cortex. These results indicate that the developmentally regulated transcription factor SOX6 may be a potential diagnostic marker for gliomas.