To investigate an apoptotic role for bcl-2 in menses, we studied bcl-2 protein production throughout the cycle. Bcl-2 protein was observed in endometrial glandular, stromal and myometrial smooth-muscle cells. Glandular cells expressed bcl-2 at proliferative through early secretory phases but not at late secretory through menstrual phases. This cyclic expression of bcl-2 gene was similar to that of oestrogen and progesterone receptors. Thus bcl-2 expression in glandular cells may be regulated by ovarian hormones. The disappearance of bcl-2 expression in glandular cells at late secretory phase was consistent with the appearance of apoptotic cells in the same phase.