In comparison with normal cervix, mitosis occur more frequently in cervical intraepithelial neoplasia(CIN) and are seen at high levels, suggesting that CIN may be associated with a progressive dysfunction in proliferative activity of cervical cells. This study aims that expression of proliferative cell nuclear antigen(PCNA) was examined to determine proliferative activity at the cell of CIN. Sixty four colposcopic biopsies from patients with cytologically and/or colposcopically dtagnosed condyloma and CIN. The cases were classified as follows ; 19 as normal cervix and condyloma, 15 as CIN I, 16 as CIN II and 14 as CIN III. Immunohistochemical detection of PCNA was performed on paraffin sections by the streptavidin-biotin peroxidase method using the monoclonal antibody PC10. There was a statisically significant correlation between the CIN grade and the PCNA grade(p<0.05). In addition, the PCNA grade showed significant correlation with mitotic grade(p<0.05) and the CIN grade was also observed(p<0.05). This study suggests that the cell proliferation index as detected immunohistochemically using PCNA may be a useful adjunct to histopathological diagnosis of various grades of CIN.