Cell proliferation of normal cervical tissues(5 cases), normal endometrial tissues(5 cases), cervical cancer tissues(8 cases), endometrial cancer tissues(10 cases) were assessed by immunohistochemical method using the monoclonal antibody Ki-67, which reacts with a nucleal antigen only in proliferating cells(late G1, S, M and G2 phase). The percentage of cells recognized with ki-67 (growth fraction) was calculated. Growth fraction was examed in 30.3±4.2% in cervical cancer tissues, 25.1±2.3% in ehdometrial cancer tissues, 19.5±2.9% in normal endometrial tissues and 9.7±2.4% in normal cervical tissues. Growth fraction in malignant cases was higher adenocarcinoma. In endometrial cancer, ki-67 positive cell rate had no relation to histological grade. This technique is quite simple and new to detect cancer cells from the point of growth potential. This result suggests that determination of growth fraction by monoclonal antibody ki-67 is useful in prognostic marker.