BACKGROUND: DNA Topoisomerase ha (Topo flu) is a nuclear enzyme whose expression levels are related to tumor cell growth and to resistance to anticancer chemotherapy. MATERIALS AND METHODS: Topo ha expression was assessed immunohistochemically in 60 surgical specimens of 47 consecutive oligodendroglioma patients. Expression levels were correlated with the MIB-1 proliferation index and with patient outcome. RESULTS: Topo flu expression ranges from 0.3 to 40.1% and is significantly associated with MIB-) staining. There is a weak trend to a higher expression of Topo flu in anaplastic oligodendrogliomas (p = 0.08). Topo ha expression is not related to patient outcome. CONCLUSION: Topo flu expression appears to serve as a marker for tumor growth in human oligodendrogliomas. The widely vaiying expression levels of Topo ha in oligodendroglioma suggest this enzyme could be used for targeted selection of patients for Topo flu-interfering chemotherapy.