Gingival overgrowth (GO) is a common side effect following administration of cyclosporin A (CsA). Various case reports have shown that squamous cell carcinomas could arise in GO induced by CsA and phenytoin. It is also known that human telomerase activated in about 90% of cancers is mainly composed of hTR, hTERT, and TPI. The aim of this study was to investigate the potential role of telomerase activity in the pathogenesis of CsA-induced GO. Included in the study were 9 patients on CsA: 4 with and 5 without GO. Gingival tissues were obtained during gingivectomy or flap procedures; gingival fibroblasts were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10,000 U/mL penicillin, 10 mg/mL streptomycin, 2 mmol/L L-glutamine, and 10% heat-inactivated fetal bovine serum at 37 degrees C under a humidified 95% air virgule 5% CO2 atmosphere. Quantitative detection of hTERT mRNA was performed with the commercially available LightCycler Telo TAGGG hTERT Quantification Kit using real-time online PCR. The hTERT mRNA expression was positive in one patient, while hTERT mRNA expression was negative in the others. Because results indicated that there may be a relationship between CsA-induced GO and positive telomerase activity, detailed studies should be performed to confirm the present findings.