The efficacy of respiratory support devices has been compromised by respiratory infection possibly related to the support mechanism itself. Differentiation between airway contamination (tracheobronchitis) and parenchymal infection (pneumonitis) is clinically significant, as is the differentiation of respiratory infection from other foci of sepsis in the complicated surgical patient. Serial quantitative tracheal cultures provide excellent objective measures of the presence, progression, and/or resolution of respiratory infection with few false positive or negative observations. Indeed, such observations often allow earlier definitive diagnosis of infection than can be achieved with conventional clinical, chemical, or roentgenographic studies. The method represents a useful supplement to the care of the patient requiring respiratory support when infection is a realistic possibility.