In women, cardiovascular morbidity and mortality sharply increase after the onset of menopause. There is substantial evidence that hormone replacement therapy (HRT) may decrease the risk of coronary heart disease; however the mechanism is unclear. We investigated the relationship between HRT and plasma viscosity as well as cholesterol levels in postmenopausal women. 30 women were using HRT (HRT users), and 30 women were not using HRT (non-users). According to the classification of their plasma cholesterol levels, 30 women were hypercholesterolemic levels (hypercholesterolemic users n = 15, and hypercholesterolemic non-users n = 15), and the others were normocholesterolemic levels. While the highest plasma viscosity was measured in hypercholesterolemic users (1.291 +/- 0.053 cP), the lowest plasma viscosity was measured in normocholesterolemic users (1.127 +/- 0.056 cP). There was a significant correlation between plasma viscosity and cholesterol levels in the women on HRT (r = 0.76, p < 0.001). We have not found a difference neither in fibrinogen levels nor in triglycerides between users and non-users.