Expression of the Wilms' tumor gene WT1 in primary astrocytic tumors was examined using a quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) or immunohistochemistry. Real-time RT-PCR showed that WT1 mRNA was expressed at various levels in all of the 25 astrocytic tumors examined. Immunohistochemical analysis showed that WT1 protein was expressed in 5 of 6 low-grade astrocytic tumors (grade l-ll) and all of 18 high-grade ones (grade III-IV), and that expression levels of WT1 protein in high-grade tumors were significantly higher than those in low-grade ones. WT1 protein was not detected in the normal glial cells contained in the tumor specimens. Furthermore, treatment with WT1 antisense oligomers specifically inhibited growth of glioblastoma cell lines, U87-MG, A172, and T-98G. These results may indicate that the WT1 gene plays an important role in tumorigenesis of primary astrocytic tumors.