To assess the transformation of cellular characteristics during a neoplastic change in uterine cervical epithelium, the populations of cells in apoptosis as well as proliferating cycle were examined in normal cervical epithelium, dysplastic change, carcinoma in situ and invasive carcinoma. The percentage of apoptotic cells (%DNA Fr.) decreased with the neoplastic change and was significantly lower in the carcinoma in situ group than in the dysplasia group. Conversely, the percentage of cells in the proliferating cycle (%GF) increased with the neoplastic change and was significantly higher in the dysplasia group than in the normal group. The ratio of %DNA Fr. to % GF was more than 1.0 in the normal group and dysplasia group, but it was less than 1.0 in the carcinoma in situ group and invasive carcinoma group. No significant correlation between %DNA Fr. and %GF was found. These results suggested to us that the decrease in apoptosis may reflect the atypical change in cervical epithelial cells during their neoplastic change, and the proliferative activity in neoplastic lesion was found when the cervical epithelium with dysplastic change was transformed to the carcinoma in situ.