Successful treatment of intrabronchial infection depends upon adequate transport of antibiotics across the blood-bronchus barrier. This paper discusses the various influences on antibiotic concentrations in the lung and describes a canine model for detailed pharmacologic studies of antibiotics in bronchial secretion. A number of factors influence antibiotic penetration into bronchial secretions, including physicochemical characteristics of the drug and such host factors as bronchial inflammation and injury. The method of antibiotic administration also influences bronchial drug levels; the highest local concentrations are associated with the highest peak values in serum. In addition, each antibiotic has a characteristic pattern of penetration into bronchial secretions. Optimal methods of antibiotic therapy for lung infection may depend on the specific minimal inhibitory concentration for the infecting organism.