We investigated telomerase expression in cervical lesions and its diagnostic value for cervical cancer and the precancerous lesions. The subjects were 100 women who underwent cervical biopsy, comprising 16 normal cervix, 61 cervical intraepithelial neoplasia (CIN) and 23 invasive cervical cancer. Telomerase activity was detected by the telomerase repeat amplification protocol using a non-radioisotope system, and quantitated using a DNA image analyzing system. Telomerase was detected at 18.8% (3/16) in normal cervix, 32. 0% (8/25) in CIN I, 50.0% (3/6) in CIN II, 60.0% (18/30) in CIN III, and 91.3% (21/23) in invasive cervical cancer. Semiquantitation of telomerase activity was significantly higher in the subjects with invasive cancer than in those with CIN or a normal cervix (p<0.05). However, telomerase activity was not significantly different between the grades of CIN. Telomerase was detected in subjects with CIN, suggesting that telomerase expression is an early event in cervical carcinogenesis. Quantitation of telomerase activity may be helpful for the diagnosis of cervical cancer.