Early detection of aetiological agents is pivotal for adequate therapy for bacterial infections. Although culture is still considered the mainstay for laboratory diagnosis, it often lacks sensitivity, especially in patients already treated with antibiotics. The present study investigated the potential clinical utility of the commercial real-time-PCR-based system SeptiFast (SF), originally intended for diagnosis of sepsis from blood specimens, in the aetiological diagnosis of other bacterial infections, in patients undergoing antibiotic therapy. A total of 53 non-blood specimens were analysed for microbial pathogen detection by conventional culture and with SF real-time PCR: 19 (35.8 %) synovial fluids, 9 (17.0 %) cardiac valve tissues and 25 (47.2 %) purulent exudates from various body sites. Overall, the number of specimens positive for a pathogen by SF (26/53; 49.1 %) was significantly greater (P=0.001) than that of specimens positive by culture (10/53; 18.9 %). In particular, SF was superior to culture for pathogen detection in cardiac valve tissues and synovial fluids. The analysis of concordance showed a fair agreement between the two methods (kappa value=0.314; 95 % confidence interval=0.531–0.097). Even with the limitation of the low number of specimens, this study confirmed the great potential of diagnosing bacterial infections by a molecular approach, and indicates that the real-time PCR SF system can be used for specimens other than blood, from patients undergoing antibiotic treatment.