Telomeres, the physical ends of eukaryotic chromosomes, are important to stabilize the chromosome and have a unique simple repetitive DNA sequence, TTAGGG in humans. In most normal somatic cells, telomere length becomes 50-100 bp shorter with every cell division, and the cells finally go into senescence, while most cancer cells have been reported to maintain the length and thus are immortalized. Telomeres are replicated by a special transcriptase, called telomerase, which is composed of a template RNA (hTR) and at least two component proteins: hTERT (hEST 2/hTRT) and hTEP 1 (hTLP 1/hTP1). In the present paper, I examined the status of telomerase activities in oral squamous cell carcinomas (OSCCs), precancerous lesions, and also cell lines established from OSCCs, by using a non-radioactive PCR-based TRAP (telomeric repeat amplification protocol) assay. Telomerase activities were detected in 23 of 30 OSCCs, 8 of 17 leukoplakias, 0 of 5 normal tissues, and in 8 of 8 OSCC cell lines and 0 of 5 normal human keratinocyte cultures. These results indicated that telomerase activity might have some association with carcinogenesis and might be used as a tumor marker in OSCC.