AIM: human telomerase reverse transcriptase (hTERT) is the catalytic subunit of telomerase, and hTERT mRNA expression contributes to telomerase activity. We therefore assessed the significance of hTERT expression in the biological behavior of giant cell tumor(GCT) of bone. METHODS: In situ hybridization was used to identify the expression of hTERT mRNA in 27 formalin-fixed paraffin-embedded clinical specimens from human GCT. RESULTS: 8 cases (8/27)displayed positive hTERT mRNA signal, positive hTERT mRNA signal located in the cytoplasms of mononuclear stromal cells and some multinuclear giant cells. CONCLUSION: The expression of telomerase in paraffin-embedded tissue can be evaluated efficiently and effectively by in situ hybridization, and the results suggest that there may be a neoplastic multinuclear giant cell type in human GCT.