The aim of this study was to evaluate enzyme-immunoassay EIA in the detection of IgA, IgM and IgG antibodies in the serological diagnosis of C. pneumoniae infection. Seventy-one patients, diagnosed as atherosclerotic heart disease and 20 patients as control group, totally 91 patients, were studied. ImmunglobulinA, IgM and IgG antibodies against C. pneumoniae were detected by EIA and micro-immunflorescence (MIF) methods. Chlamydia pneumoniae IgM positivites were 12% with both of EIA and MIF; IgA positivities 52% with EIA and 44% with MIF; IgG positivities 85.3% in with EIA and 45.3% with MIF. It was concluded that, because of EIA is genus-specific, new species-specific commercial kits are needed for the serological diagnosis of chronic C. pneumoniae infection.