||Although much work has been done by many investigators in the study of emphysema, the etiology and the pathogenesis of emphysema are still unknown. Therefore, a study was made to investigate the bacterial flora of patients with emphysema, to see if there was a species or strain of organisms peculiar to emphysema. These bacteria were tested (1) for their ability to multiply in pulmonary mucus in vitro, (2) to examine the surface tension properties of mucus in vitro, and (3) to examine the alteration of surface tension of culture media by microorganisms. Twenty-six patients from the Pulmonary Disease Service of the Veterans Administration Hospital, Salt Lake City, Utah were utilized in this study. An initial selection of patients known to have bronchitis, bronchiectasis, or emphysema and who did not have antibacterial chemotherapy for 6 months were chosen by the Chief of the Pulmonary Disease Service and resident physicians. Most studies of the sputum flora in patients with chronic bronchitis and bronchiectasis are based on bacteriological cultures of expectorated bronchial secretions. Contamination by nasopharyngeal microorganisms is inevitable, since bacteria known to be normal inhabitants of the pharynx are cultured from expectorated sputum. Bacteria isolated in this manner cannot be assumed to have significance in bronchial inflammation. This study was designed to compare qualitatively and quantitatively the bacterial flora of expectorated bronchial secretions and saliva in patients with chronic bronchitis or bronchiectasis, in an effort to assess the importance of contamination of the expectorated bronchial secretion by saliva. A comparison of the numbers of bacteria in saliva and sputum in 26 patients showed that there are tremendous numbers of bacteria in saliva. Even in a clean" mouth, saliva contained as large or larger numbers of bacteria than did expectorated sputum. The presence in both sputum and saliva of alpha hemolytic Streptococci, non-hemolytic Streptococci, the Neisseria species, non-hemolytic Staphylococcus aureus and non-hemolytic and hemolytic St. albus suggests a nasopharyngeal origin of these strains. The D. pneumoniae, hemolytic St. aureus, and the Hemophilus species were less frequently isolated from the sputum suggesting a bronchial origin for these organisms. Besides using the cultural technique for the isolation of D. pneumoniae, white mice were inoculated with saliva and sputum. It was found that animal inoculation yielded more positive isolations than by cultural methods in saliva. However, there was a greater number of isolation of D. pneumoniae by cultural technique from the sputum than by animal inoculation. Sterile sputum was employed as a substrate for the possible growth of bacteria from patients with emphysema, and it was found that some of these bacteria grew well in sputum. The surface tension measurements of sputa and broths were performed before and after incubation with organisms. This investigation has shown that the proliferation of microorganisms in sputum or broth either increased or decreased the surface tension of the sputum or broth depending on the bacteria.