Chlamydia pneumoniae is an intracellular pathogen and an important cause of respiratory tract infections in humans and more recently it has been associated with chronic diseases such as atherosclerosis. Numerous studies have been performed to show the "infectious" hypothesis of atherosclerosis by direct detection of the organisms within atheromatous plaques by seroepidemiological estimation and by animal, immunological and antibiotic interventional studies. In this work we investigated the relation between chronic chlamydial infection, inflammatory markers, Interleukin 7 (IL-7) production and coronary heart disease. We studied 60 patients with coronary heart diseases (CHD), 45 of whom were men and 15 women, with a mean age of 65+/-5 years, and a control group of 20 healthy subjects, 15 men and 5 women, with a mean age of 60+/-7 years. Detailed histories including symptoms, risk factors and demographic data were obtained from patients and healthy subjects by administering a standardized questionnaire. Our results demonstrate that the enzyme-linked immunoassay (ELISA) test appears to have a greater sensitivity than the microimmunofluorescence (MIF) technique. 80% of patients had positive IgG to C. pneumoniae and 58% positive IgA to C. pneumoniae with ELISA, while the MIF test showed 68% and 55% positive IgG and IgA to C. pneumoniae, respectively. The control subjects showed 55% positive IgG and 10% IgA to C. pneumoniae by ELISA and 35% positive IgG and 5% IgA to C. pneumoniae by MIF. The combination of positive IgG and IgA to C. pneumoniae was present more frequently than in the control group. Serum levels of IL-7 measured by ELISA were also significantly higher in patients compared to healthy subjects. In conclusion, our study shows that C. pneumoniae IgG and IgA seropositivity, inflammatory markers such as IL-7, fibrinogen, C-reactive protein were significantly correlated with CHD.