A patient is described in whom there developed a pulmonary infiltrate and constrictive pericarditis caused by a combined Actinomyces and Actinobacillus actinomycetemcomitans infection, presumably originating from his poor dentition. The diagnosis was only made following repeated thoracotomy. After surgery, long-term treatment with antibiotics led to complete clinical recovery. None the less, some months later he was found to have a brain abscess which resolved during a further course of antibiotics. The variable clinical picture of actinomycosis is discussed, as well as the role of other bacteria frequently associated with actinomycotic infection, in particular Actinobacillus actinomycetemcomitans. The therapeutic implications are described.