In 193 reviewed cases of pleuropulmonary infections involving anaerobic bacteria, the predominant clinical syndromes were aspiration pneumonia, lung abscess, and empyema. Most patients had an indolent infection with tissue necrosis (abscess or bronchopulmonary fistula) at initial presentation. Nevertheless, many had a more fulminant disease course resembling that of pneumococcal pneumonia. Transtracheal aspiration was the procedure most commonly used to obtain uncontaminated specimens for anaerobic culture; since this procedure now is seldom employed, pulmonary infections due to anaerobes rarely have an etiologic diagnosis at present. The dominant pathogens are Peptostreptococcus, Bacteroides, Prevotella, and Fusobacterium species. Although clindamycin is widely considered to be the antibiotic of choice, proper therapeutic trials would probably prove many antibiotics to be effective for the treatment of anaerobic pleuropulmonary infections.