To evaluate the effect of conjugated equine estrogens (CEE) plus medroxyprogesterone acetate (MPA) and raloxifene on serum levels of complement C3 and C4 fractions in postmenopausal women.Twenty healthy postmenopausal women were studied. In all weight, height and body mass index (BMI) were documented. FSH and estradiol levels were measured. They were randomly divided into two groups, according to the treatment they received: group I, CEE 0.625 mg/day plus MPA 2.5 mg/day (n = 7); group II, raloxifene 60 mg/day (n = 13), both treatments were continuous. Serum levels of C3 and C4 complement fractions were measured by immunonephelometry at baseline and six months after start of treatment. Differences among groups of baseline and final C3 and C4 levels were measured with Student's t test for independent and paired samples, respectively.There were no differences among groups in age, weight, height and body mass index, neither in C3 and C4 levels among baseline and final levels when comparing each group separately.Complement may not intervene significantly in the atherosclerotic inflammatory process in women receiving CEE plus MPA or raloxifene.