Chlamydia pneumoniae has been shown to be an important and common respiratory pathogen in humans. Although the role of Chlamydia pneumoniae as a cause of Pneumonia has been established, the potential importance of Chlamydia pneumoniae infection in patients with chronic obstructive pulmonary disease has not been defined. Serology is currently the tool used most often for routine diagnosis of recent Chlamydia pneumoniae infections. The standard serological technique at this moment is the MIF test. However it has a significant subjective component and requires experience and skill to interpret the fluorescence patterns. The use of ELISA is easier and more objective but its sensitivity and specificity were controversial.The primary goal of this work is to study the possible association between Chlamydia pneumoniae and chronic obstructive pulmonary disease and to evaluate the usefulness of rDNA LPS ELISA Compared to MIF as a Gold standard for diagnosis of Chlamydia pneumoniae infections.We conducted this study on 30 cases with established chronic obstructive pulmonary disease patients who were further divided into two groups according to the severity of the disease. They were investigated for Chlamydia pneumoniae antibodies Ig G & Ig M by MIF test and ELISA. We also investigate 30 normal age and sex matched persons (control group) for Chlamydia pneumoniae antibodies by MIF and ELISA.Using the MIF test, the incidence of acute Chlamydia pneumoniae infections in the chronic obstructive pulmonary disease was 16.6 % (5 out of 30) compared to 10 % (2 out of 30) in the control. While the incidence of previous exposure was 66.6 % (20 out of 30) compared to 60 % (18 out of 30) in the control. By the ELISA test, a lower incidence of the acute (6.6 %) and a higher incidence of the previous exposure (73.3 %) compared to the MIF test results.By the ELISA or the MIF test (each separetely), the incidence of infection and the prevalence of antibody and its geometric mean titre were higher in the severe cases than in the mild to moderate cases and lowest in the control group. While the difference between the patient and control group was statistically insignificant.By taking the MIF test as a gold standard, it was found that the sensitivity of the ELISA is 37 % and its specificity is 98 %. This results demonstrates that the use of rDNA LPS ELISA does not appear to be sufficient sensitive for diagnosing Chlamydia pneumoniae infections.In conclusion, a Chlamydia pneumoniae infection does not appear to play an important role in the pathogeneses of chronic obstructive pulmonary disease as there is no significant difference in the statistical analysis between the patient and control group. However further studies on a large scale should be done to confirm these findings. Also the use of rDNA LPS ELISA does not appear to be sufficient sensitive for diagnosing Chlamydia pneumoniae infections especially with the use of single serum sample. So the use of paired serum samples two to three weeks apart is very important in the diagnosis of Chlamydia pneumoniae by rDNA LPS ELISA and that ELISA Ig M alone is not sufficient to determine the acute infection.