The incidence of ischaemic heart disease (IHD) is higher in postmenopausal women than in premenopausal women of the same age. The difference may be partly explicable in terms of differences between premenopausal and postmenopausal women in haemostatic function. This possibility has been studied in 833 White women in the Northwick Park Heart Study (NPHS). Mean levels of factor VIIC, fibrinogen, and cholesterol were between 6% and 10% higher in postmenopausal women than in premenopausal women of the same age. When allowances were made for associations between these variables, the difference between the two groups in cholesterol was no longer evident. By analogy with NPHS data on men, the differences in factor VIIC, fibrinogen, and cholesterol would increase the risk of fatal IHD in postmenopausal women by about 40% compared with the risk in premenopausal women of the same age.