Chlamydia pneumoniae is a common pathogen in the world often causing upper or lower respiratory tract infection and may also be linked to some chronic inflammatory diseases. Recent studies have shown that a high percentage of healthy blood donors harbour Chlamydia DNA and antigens. The objective of this study was to investigate the presence of this microorganism among blood donors. Blood samples were collected between November 2004 and March 2005 from 196 healthy blood donors. Ten millilitre of blood was collected in ethylenediaminetetraacetic (EDTA) tube. Reverse transcription of RNA was performed with Moloney murine leukaemia virus (MMLV) reverse transcriptase and random primers hexamer. Polymerase chain reaction products were evaluated by electrophoresis. Data were analysed using the chi(2) test and t-test. Of the 196 healthy blood donors, 7.1% were C. pneumoniae DNA positive (CI 95 % = 3.51- 10.69), which is slightly higher in female (8.5%) than male (6.5%) donors; this difference was not found to be significant (P = 0.4). The average age of study groups was 40.84 (SD +/- 10.80) years; significant association was not found between age groups and the presence of C. pneumoniae DNA. There was no significant differences between positive rate and first-time [37 (19.3%)] and repeat [155 (80.7%)] donors. C. pneumoniae DNA seems to be frequent in apparently healthy blood donors; therefore, it can be a threat for blood safety. But further studies are needed to evaluate the survival of C. pneumoniae in blood bank conditions and in blood recipients to define the clinical importance of such findings. Elimination of intracellular bacteria by filtration is an effective strategy for risk reduction.