In order to explore the long-term effect of hormone (17 beta-oestradiol) substitution therapy on blood pressure in healthy post-menopausal women, we reviewed the data from five long-term (1-2 yr), double-blind, placebo-controlled studies carried out in our department over the last decade. Three of the studies related to early post-menopausal women (mean age 50 in all three cases) and two involved later post-menopausal women (mean ages 64 and 70, respectively). The systolic blood pressure values during hormonal substitution therapy showed no change in relation to those recorded during placebo administration, whereas the diastolic blood pressure fell slightly in all five studies. However, in that based on the oldest subjects, the results were not statistically significant. It was therefore concluded that hormone substitution therapy with 17 beta-oestradiol has no adverse effect on blood pressure, and may even have a beneficial action.