To identify changes in haemostatic balance during continuous oestradiol-progestogen treatment, 60 postmenopausal women with climacteric complaints, mean age 55.4 years (range 44-68) were randomly allocated to receive one of four hormone replacement regimens for one year. All four formulations were administered daily and continuously, each contained 2 mg of 17 beta-oestradiol in combination with either norethisterone acetate, 1 mg (group A) or 0.5 mg (group B) or megestrol acetate, 5 mg (group C) or 2.5 mg (group D). No significant changes occurred during treatment within or between the groups in platelet count, fibrinogen and 2-antiplasmin. Activated partial thromboplastin time was shortened (P less than 0.05) in group D and a decline in factor VII activity and antigen (P less than 0.001) and in ATIII activity (P less than 0.05) was noted in group A. Protein C tended to decline in all treatment groups but statistically significant changes were noted only in groups A and C. Two women developed crural thrombosis during the observation period.