BACKGROUND AND OBJECTIVES: To evaluate the association between chronic infection with Chlamydia pneumoniae, as measured by Immunoglobulin G and A, and acute myocardial infarction (AMI) in Korea. MATERIALS AND METHODS: A total of 136 patients [normal control 65 cases (male:female 27:8, mean age 55.1+/-11.7 years), AMI 71 cases (male:female 54:17, mean age 58.9+/-12.7 years)] had immunoglobulin G, A, and M antibody titers measured against Chlamydia pneumoniae by microimmunoflorescence assay and had coronary angiography performed. We investigated the incidence of major adverse cardiac events (MACE) at 6 month follow-up. Controls were defined as patients with no significant stenosis on coronary angiography. RESULTS: 1) AMI patients were more likely to be male (76.1: 41.5%) and smokers (67.6: 16.9%) compared with the controls. >2) In AMI patients, there was a weak correlation with IgG and IgA antibody titers (r=0.39, p=0.001).> 3) After adjusting for gender and smoking status, IgG and IgA antibody titers were similar between two groups.> 4) Increased IgG and IgA titers did not affect the MACE during follow-up. CONCLUSION: Chronic Chlamydia pneumoniae infection detected by immunoglobulin assay is not significantly associated with AMI. Further studies, such as polymerase chain reaction, immunocytochemistry, or culture of the atheromatous plaques, are needed to better define the association.