The anaerobic syndromes of gas gangrene and tetanus are due to systemic intoxications that develop following infection with clostridia at some site of trauma. Classically, these conditions developed as complications of accidental trauma, the spore-forming anaerobes being derived from the inanimate environment. While tetanus remains typically an exogenously derived disease, gas gangrene more frequently presents as an endogenously derived complication of elective surgery. Their treatment is briefly discussed, including the role of antimicrobial therapy. During the last decade there has been an increasing awareness of the importance of non-sporing anaerobes as a major cause of serious endogenously derived infections in man. They are not only a common cause of postoperative infection following appendicectomy, and acute and elective colorectal and gynaecological surgery, but they also cause a wide variety of infections at other sites, usually secondary to some preexisting pathology. In the management of these infections, surgical drainage of pus, when present, is of first importance. Systemic antimicrobial therapy, directed against the anaerobes is dramatically effective both in the management of established infections, and in their prevention in patients known to be at risk.