PURPOSE: Chlamydia pneumoniae (CP) infection seems to be related to atherosclerotic diseases. A prospective sero- epidemiologic study was performed to analyze the relationship between CP infection and peripheral vascular disease in Korean patients. The aims of this study were to find the prevalences of CP antibody in the serum and CP antigens in the vascular tissues, and to analyze the differences between several disease groups. METHODS: Our subjects included a total of 61 patients (76 vascular tissues) who had undergone operative procedures for peripheral vascular diseases. They were classified into 3 groups: Group 1; 14 abdominal aortic aneurysm, Group 2; 15 atherosclerosis obliterans, and Group 3; 32 varicose vein cases. The CP antibody titers were determined using the microimmunofluorescence test (MIF) and the CP antigen in the vascular tissues with a semi-nested polymerase chain reaction (PCR) and an in situ hybridization technique (ISH). RESULTS: The prevalences of chronic or past CP infection from the MIF (IgG antibody titer > or = 1: 32) in Groups 1, 2 and 3 were 78.6, 73.3, and 68.8% respectively, but with statistically significant differences. The prevalences of PCR- positive tissues in Groups 1, 2 and 3 were 21.4, 6.7, and 0% respectively. There was no CP DNA detected in the venous tissue. CP DNA was detected more frequently in aneurysmal disease than atherosclerosis obliterans, but this was not statistically significant(p=0.265). In comparison with the varicose veins, aortic aneurysms showed a significantly higher PCR positivity ratio (p=0.002), and a similar result was seen with ISH. There was no relationship between CP antigen positivity and the known risk factors for atherosclerosis. CONCLUSION: A high prevalence of CP antibodies was observed in the serum of Korean patients with vascular disease, which matched that in western populations. CP DNA was also detected in atherosclerotic tissues, which was especially high in aneurysmal disease, implying a possible causative role of CP infection in the pathogenesis of the atherosclerotic disease. This is the first report on the prevalence of CP in vascular tissues in Korean population.