The bcl-2 gene product inhibits programmed cell death (apoptosis). The expression of this protein has been examined in normal endometrium and found to be cycle dependent with consistent expression in the proliferative phase. In the current report, bcl-2 gene expression was examined in 88 endometrial biopsies that showed 99 histologic patterns ranging from proliferative endometrium to carcinoma. Whereas expression was always detected in 17 samples of proliferative endometrium, eight cases of simple hyperplasia, and five cases of complex hyperplasia, expression was detected in only five (42%) of 12 atypical hyperplasias and in only 27 (47%) of 57 carcinomas. In atypical hyperplasia and carcinoma showing expression, both staining intensity and distribution were less than that seen in their benign counterparts. Three of five biopsies showing both benign endometrium and carcinoma showed positivity in benign but not in malignant glands. In endometrial carcinoma, bcl-2 expression did not correlate with grade, stage, or survival. In addition, in cases of carcinoma, a negative correlation between bcl-2 and p53 expression, which has been reported in other tumors, was not observed in this study. The invariable expression of bcl-2 in proliferative endometrium suggests that this protein may be important for cell survival. Its role in preventing cell death, however, appears to be frequently bypassed in atypical hyperplasia and endometrial carcinoma possibly by other factors impeding programmed cell death. Thus, if an apoptotic pathway usually blocked by bcl-2 expression would not necessarily lead to cell death. Defects in an apoptotic pathway such as the transforming growth factor-beta pathway, which can be blocked by bcl-2, may possibly account for the phenomenon observed in this study.