Telomeres are specialized structures found at the ends of eukaryotic chromosomes. Telomeres contain tandem repeated G rich sequences, such as TTAGGG and stabilize the chromosome and protect DNA from illegitimate recombination and may aid in chromosome attachment to the nuclear membrane. Telomerase is a ribonucleoprotein, a RNA dependent DNA polymerase and acts as a reverse transcriptase-like enzyme which maintains telomere length by adding telomeric repeat units of TTAGGG to the telomeric end, and this has been found only in cells with unlimited replicative potential such as sperm cells, immortalized cell lines and cencer tissues, but not in normal somatic cells. Telomerase is believed to be one characteristic and may be the best indicator of cell immortality. To assess the role of telomerase in the development of malignant transformation of head and neck cancer, we have measured telomerase activity in head and neck cancer tissues and corresponding normal tissues using a recently developed sensitive PCR-based telomerase assay (telomeric repeat amplification protocol : TRAP). Sixteen of 18 cancer tissues were positive for telomerase actibity, whereas corresponding normal tissues were negative for telomerase activity. These findings suggest that telomerase may play a key role in the establishment and progression of the head and neck cancer.