Aim: To determine if inhibitors in blood and respiratory specimens influence the polymerase chain reaction (PCR) results for Streptococcus pneumoniae in patients with community-acquired pneumonia (CAP). Patients and methods: The study included 80 patients with CAP. In addition to conventional microbiological methods, PCR for fragment of pneumolysin gene in serum (N=77) and BAL (N=19) specimens was also performed. The presence of PCR inhibitors in specimens was determined with spiking and inhibitors were removed by diluting the specimens. Results: With all methods, S. pneumoniae was detected in 25 (31,3 %) of patients with CAP. PCR results in 77 serum specimens were negative. PCR inhibitors were detected in one serum specimen. BAL specimens were PCR-positive in three patients and there were no inhibitors detected. Discussion: When planning and performing PCR on clinical specimens, PCR inhibitors should be considered as a possible cause of false-negative results. Several procedures are used to remove PCR inhibitors from clinical specimens or to diminish their influence (extraction method, optimizing DNA amplification, diluting of specimens). Presence of inhibitors can be determined by adding of an internal control to each specimen or with spiking. Conclusions: In this study the presence of inhibitors was determined in only one serum specimen. It can be concluded that PCR inhibitors in serum and BAL specimens do not influence the PCR results for S. pneumoniae in patients with CAP.