Conflicting data exist concerning the value of antimicrobial prophylaxis in chest trauma. In a prospective and randomized study, we assessed the value of antibiotic prophylaxis in 80 consecutive relatively young, predominantly male patients admitted for gunshot or knife injuries of the chest. Forty patients received intravenous doxycycline and 40 received no antibiotic. Between the two groups we found no difference in the incidence of postoperative infections: we conclude that routine antibiotic prophylaxis is not recommended in penetrating chest trauma in patients such as ours.