The proliferation rate (as assessed by Ki67 expression) and expression of oestrogen-regulated progesterone receptor (PR) was studied in normal post-menopausal breast epithelium. Normal breast epithelium from patients receiving hormone replacement therapy (HRT) at the time of surgery containing either oestrogen alone (E2) or oestrogen and progesterone combined activities (E2 + P) was also studied, as HRT has been linked to an increased breast cancer risk. Samples of breast tissue, containing normal epithelium, from 185 patients undergoing surgery for benign or malignant disease were immunocytochemically stained for PR and Ki67. The percentage of labelled cells was expressed as the labelling index (LI). The median Ki67 LI in normal post-menopausal breast epithelium was 0.19 and median PR LI was 4.75, and both were unaffected by patient age, duration of menopause or if the tissue sample originated from a breast with benign or malignant disease. Proliferation did not alter significantly in patients taking HRT (P = 0.61); however, PR expression was up-regulated in both E2 and E2 + P users (P = 0.01). The dose and duration of HRT had no effect on either parameter. A possible attenuation of sensitivity to oestradiol-induced proliferation but not to PR expression occurs in the post-menopausal breast.