Inward rectifying potassium channels (Kir), and in particular Kir 4.1, are key regulators of glial functions, which in turn determine neuronal excitability and axonal conduction. A high expression of Kir 4.1 has been detected in in some pathological conditions. In this study, we investigated the expression of Kir 4.1 mRNA and protein in 80 cases of human astrocytic tumors by reverse transcription polymerase chain reaction, Western blot and immunohistochemistry, respectively. The correlation between Kir 4.1 expression and pathologic grade of astrocytic tumors was further analyzed. The results showed that the expression of Kir 4.1 mRNA and protein, as well as the Kir 4.1 immunoreactivity score (IRS), increased markedly with increasing pathologic grade. Therefore, Kir 4.1 may be a new biomarker for astrocytic tumors. It may also be an attractive therapy target for human astrocytic tumors. (c) 2008 Elsevier Inc. All rights reserved.