Persistant infections due to Chlamydophila pneumoniae, Helicobacter pylori, and Cytomegalovirus are suggested to contribute to the development of atherosclerosis. In this study, the presence of these agents was investigated by polymerase chain reaction (PCR) and serological tests in atherosclerotic plaques and non-atherosclerotic vessel samples. Thirty-three specimens from the atherosclerotic plaques (lesion group), 45 specimens from the healthy left internal mammarian arteries and ascending aortas of the atherosclerotic patients (non-lesion group), and 15 specimens from the aortas of non-atherosclerotic patients as determined by angiography (control group), were included to the study. Serum samples were also collected from all study subjects for the serological investigation. PCR and ELISA were used in order to determine the nucleic acid positivity and IgG titers, respectively. C. pneumoniae and H. pylori DNA were found in 6 (18.1%) and 14 (42.4%) of the lesion group, 2 (4.4%) and 9 (20%) of the non-lesion group, respectively. CMV DNA was not found in either groups. All of the PCR results of control group were negative. C. pneumoniae IgG was found positive in one case of the lesion group (3%) and three cases of the non-lesion group (6.7%). H. pylori IgG were positive in all the subjects except for three patients who were in the non-lesion group. The presence of C. pneumoniae and H. pylori DNA in a considerable number of lesion and non-lesion groups' specimens, but absence in control group specimens supports the hypothesis that these agents have an association with atherosclerosis.