Serum C3, C4, IgG and IgM levels were evaluated in healthy post-menopausal women receiving short-term hormone replacement therapy (HRT) regimens and in untreated women. Serum C3, C4, IgM and IgG levels were assessed in 54 women receiving HRT therapy (CEE 0.625 mg+MPA 2.5 mg/day), and in 54 control women not receiving HRT. The results showed that the mean serum C3 and C4 levels were significantly higher in women receiving HRT than those untreated women (P＜0.01). There was significant difference in lgG and IgM levels between two groups. It was con-cluded that HRT might be involved in the development of cardiovascular diseases through inflamma- tory mechanisms, as suggested by increased serum levels of C3 and C4.