AbstractBradykinin may act as a promoter of endometrial regeneration. Bradykinin-like immunoreactivity was detected immunocytochemically in the glandular epithelium and stroma of human endometrium. The staining was localized around the stroma and especially in the cells undergoing mitosis. Relatively weak staining was seen in the stromal cells of secretory endometrium, which was predominantly localised around the basal vacuoles of endometrial glands. During the late secretory phase, the intensity of staining was diminished throughout the endometrium: the glandular epithelium showed weak staining and stroma appeared negative. As phosphatidate, the product of phospholipase D pathway, may mediate cell proliferation, the effect of 17β-oestradiol on bradykinin-evoked phospholipase D activity assayed as accumulation of [3H]phosphatidylbutanol ([3H]PtdBut) was examined in [3H]myristic acid-labelled primary cultures of human endometrial stromal cells. Bradykinin induced a rapid accumulation of [3H]PtdBut in a time-dependent manner, indicating phospholipase D activation. Pretreatment of stromal cells with 17β-oestradiol enhanced the bradykinin-evoked phospholipase D activity. These results suggest that bradykinin-like immunoreactivity is strongly associated with proliferative stromal cells undergoing mitosis, a process that may be mediated by phospholipase D activation as the magnitude of this enzyme's activationin vitroappears to be regulated by 17β-oestradiol.