The bcl‐2 proto‐oncogene, which inhibits programmed cell death (apoptosis), has recently been found to be cyclically expressed in human endometrium. In order to investigate its role in endometrial hyperlasia and neoplasia, bcl‐2 expression was studied in 25 cases of endometrial carcinoma and 20 cases of endometrial hyperplasia (eight simple, two complex, and ten atypical hyperplasias). Uniform intense cytoplasmic bcl‐2 expression was found in all cases of non‐atypical hyperplasia, and less strong positivity in eight out of ten cases of atypical hyperplasia. In well‐differentiated carcinomas, nine out of ten showed weak to moderate bcl‐2 expression, whereas six out of seven poorly differentiated carcinomas were bcl‐2‐negative. Moderately differentiated tumours were an intermediate group, with six out of eight being positive. Widespread localization of bcl‐2 protein to the chromosomes of dividing cells was also demonstrated, regardless of cytoplasmic bcl‐2 expression, with rare staining of interphase nuclei. Our findings suggest a role for bcl‐2 in the natural history of endometrial neoplasia and studies are needed to determine its usefulness as a prognostic marker. The finding of bcl‐2 localization to chromosomes has important implications for its mode and site of action.