Here we report an immunohistochemical analysis of P2X4 receptor (P2X4R), an ATP-gated ion channel, expression in rat C6 glioma model. Striking P2X4R expression was detected in compact and infiltrative tumor growth areas. Expression of P2X4R by perivascular cells was observed in normal control brain and in brain areas not affected by tumor growth. Double-immunolabeling revealed that P2X4R was co-expressed by ED1+, AIF-1+, and EMAP II+ tumor-infiltrating microglia/macrophages; whereas on GFAP+ and nestin+ astrocytes P2X4R was hardly seen. Our results indicate that P2X4R expression defines a distinct subset of tumor-associated macrophages and activated microglia in glioma.