A 63-yr-old man developed pericardial effusion with tamponade after transbronchial needle aspiration (TBNA) of a subcarinal mass. A diagnosis of polymicrobial bacterial pericarditis was made when pericardiocentesis revealed purulent fluid that grew a mixed culture of anaerobes and aerobes, organisms that constitute part of the normal upper respiratory tract flora. To examine the possibility that contamination of the transbronchial needle (TBN) could lead to purulent pericarditis by inoculation of bacteria into the mediastinum, quantitative cultures of the TBN content were performed in seven consecutive patients. Abundant growth of multiple anaerobic and aerobic organisms was demonstrated in all seven cultures. We conclude that subcarinal TBNA is another potential cause of purulent pericarditis. This results from upper respiratory tract contamination of the open distal end of the TBN as it passes through the suction channel of the bronchoscope.