Recent studies suggest the association of atherosclerotic cardiovascular diseases with Chlamydia pneumoniae infection in western populations. It is of great interest whether such an association exists in Asians with their distinct genetic background. Symptomatic patients with coronary heart disease (29) or arteriosclerosis obliterans (10) who underwent directional endo-atherectomy were studied. Atherectomy specimens of coronary and iliac arteries were examined for C. pneumoniae by culture, nested PCR and immunohistochemical stain (IHC) with one Chlamydia genus-specific, two C. pneumoniae species-specific, and two C. trachomatis species-specific monoclonal antibodies. Among the 29 patients with coronary artery disease, C. pneumoniae was detected in the coronary arteries of 13 by IHC, 16 by PCR and 20 by IHC or PCR, or both. C. pneumoniae was also found in the iliac arteries of four patients by IHC, three by PCR and five by IHC or PCR, or both, of the 10 patients with arteriosclerosis obliterans. Attempts to isolate C. pneumoniae by culture were unsuccessful. The re-stenotic rate after atherectomy was higher in the C. pneumoniae-positive group than in the negative group, but not significantly so. These findings support the high incidence of C. pneumoniae in atherosclerotic lesions of symptomatic patients with coronary heart disease and arteriosclerosis obliterans in Asians.