Chlamydia pneumoniae has been associated to coronary artery disease by various methods including recovery of viable bacteria from plaques. The pathogenetical relevance of this is unclear but investigation of antichlamydial therapy in coronary arteriosclerosis is already in progress. The microimmunofluorescence test (MIF), the only species-specific serological assay available, might be considered useful in identifying patients with vascular chlamydial infection. However, this has never been systematically examined. We compared levels of C. pneumoniae antibodies in sera using MIF with direct detection of C. pneumoniae in coronary artery segments from 158 patients undergoing myocardial revascularization. A polymerase chain reaction (PCR) protocol, recently evaluated for use with vascular materials, detected C. pneumoniae infection in 34 patients. Correlation of serology and PCR was poor: in relation to PCR. MIF-IgG analysis had 21% sensitivity, 90% specificity, 37% positive predictive value, and 81% negative predictive value for detection of chlamydial presence. Thus, the MIF test currently appears not suitable to predict individual vascular C. pneumoniae infection.