Objective : To investigate the distribution of bcl-2 and bax proteins in the endometrial neoplastic tissues in order to find out the role of these two genes in causing the neoplasia.Methods: Formalin-fixed, paraffin-embedded tissue blocks were retrieved from the surgical pathology files of the Department of Pathology, College of Medicine, Yonsei University, for the period from 1992 through 1997. We selected cases of endometrial hyperplasia without atypia(n=30), hyperplasia with atypia(n=10), and endometrial adenocarcinoma, grade I(n=23), grade II(n=15), grade III(n=11). Immunohistochemical staining was performed to detect the expression of bcl-2 and bax proteins. Results : Bcl-2 was expressed in all cases of endometrial hyperplasia without atypia(100.0%). In endometrial hyperplasia with atypia, bcl-2 was expressed in 7 cases out of 10 cases(70.0%). The intensity of bcl-2 was stronger in hyperplasia without atypia. Bax was expressed in 29 cases out of 30 cases in endometrial hyperplasia without atypia(96.7%). In endometrial hyperplasia with atypia, bax was expressed in 6 cases out of 10 cases(60.0%). The expression, the intensity, and the percentage of positive tumor cells of bcl-2 were decreased as the grade advanced in endometrial adenocarcinoma. However, there was no difference in the expression of bax. Conclusion : Bcl-2 and bax may play a role in keeping transformed cells alive in premalignant endometrial lesion. Furthermore, bcl-2 may be involved in the differentiation of the endometrial cancer cells and may be used as a prognostic factor in endometrial cancer.