The aim of this study was to investigate whether blood-based polymerase chain reaction could serve as a diagnostic tool to identify individuals with acute respiratory Chlamydia pneumoniae infection. Respiratory specimens and peripheral blood mononuclear cells of 58 patients were analyzed using nested polymerase chain reaction and cell culture. Fifteen patients were polymerase chain reaction-positive for Chlamydia pneumoniae. Nine patients were positive in only the respiratory specimen; two in both the respiratory and blood sample (time intervals between onset of symptoms and sample collection, 3-10 days and 3-4 weeks, respectively); and four in only the blood sample. Detection of Chlamydia pneumoniae DNA in peripheral blood mononuclear cells does not seem to be a suitable marker for acute respiratory Chlamydia pneumoniae infection.