Objective To investigate the assay for detection of chlamydia pneumoniae (cpn) DNA in the peripheral blood mononuclear cell using nested polymerase chain reaction (nPCR).Methods Peripheral blood mononuclear cells(PBMC) were collected by using lymphocyte Ficoll and the low-osmotic hemolysis method.Cpn DNA was examined with nPCR.All 150 patients with coronary heart disease (CHD) were confirmed by angiography,and another 55 clinical CHD patients with normal angiography were characterized as control.Results Chlamydia pneumoniae DNA was detected in 49 (32.7%) of 150 patients with CHD and in 1 (1.8%) of 55 of control group.The positive rate of nPCR in CHD groups was significantly higher than those in control group.OR was 26.2 and 95%CI (confidence interval) was 3.52-194.98.Conclusion PBMC sample could be collected easily.The nPCR is sensitive and specific method,and could be used for clinical diagnosis of Cpn infection in coronary heart disease patients.