Results from this study of 16 patients who underwent extractions and alveoloplasty indicate that cephalexin effectively penetrates alveolar bone. After cephalexin had been administered, 500 mg four times a day for 48 hours, the average concentration in bone exceeded the average minimal inhibitory concentration of six organisms commonly encountered in infections and bacteremias of dental origin. These data and the current knowledge of cephalexin suggest that cephalosporins may have a unique use in dental infections or potentially harmful bacteremias caused by susceptible organisms.