OBJECTIVE To assess the changes, over a 6-month period, in serum lipoproteins, apoproteins and coagulation factors, induced in post-menopausal women treated by a new transdermal oestradiol patch. METHODS Fifty-three hysterectomised, healthy, post-menopausal women were treated by a new transdermal patch designed to deliver 50 micrograms of 17 beta oestradiol per day (Gynaderm, Shire Developments). One patch was applied twice weekly. RESULTS Forty-two patients completed the study. There was no significant change in the level of total cholesterol, triglycerides, HDL or LDL. There was a significant rise in the level of ApoAI after 3 months on therapy but this was not sustained after 6 months; there was also a significant drop in the level of ApoAII after 6 months on treatment. The changes in ApoB and Lp(a) were not statistically significant. There was a significant drop in the level of antithrombin III and of protein S, and a significant rise in factor VII. The drop in the level of fibrinogen and of protein C were not statistically significant. CONCLUSIONS The transdermal route of oestradiol administration causes minimal changes in lipoprotein metabolism. The statistically significant changes in the thrombophilia profile parallel those observed with oral HRT, but, similarly, may not reflect clinical significance. The potential of transdermal oestrogens as cardioprotective agents is yet to be determined.