This study compared the effects of oral estradiol (E2) with either medroxyprogesterone acetate (MPA) and micronised progesterone on risk biomarkers for breast cancer in a post-menopausal primate model. 26 ovariectomised adult female cynomolgus macaques were divided into groups and rotated randomly through treatments of placebo, estradiol (1mg/day), estradiol + progesterone (200mg/day), and estradiol + medroxyprogesterone acetate (2.5mg/day). All treatments were administered orally for a period of two months and separated with a wash-out period of one month. Breast epithelial proliferation was measured by Ki67 expression. Compared to the placebo, estradiol + MPA administration resulted in significantly greater breast proliferations, whereas estradiol + progesterone did not. Overall this suggests that oral micronised progesterone has a more favourable effect on risk biomarkers for menopausal breast cancer than MPA.