Exacerbations of bronchial asthma that cannot be accounted for by allergic reactions have sometimes been called "infective" asthma. The validity of this designation was tested by study of transtracheal aspirates (TTA) obtained from 27 asthmatic patients in relapse who had findings suggestive of respiratory infection and 12 subjects without respiratory disease. Aspirates were cultured for aerobic and anaerobic bacteria, Mycobacteria, fungi, Mycoplasma, and viruses. A comparable variety of bacterial and fungal growth in small numbers was obtained from a majority of both groups. Microbial growth did not correlate with the presence of symptoms or signs compatible with infection. Aspirates from asthmatics with chronic bronchitis, immediate hypersensitivity to aeroallergens, or aspirin intolerance yielded no greater growth than did aspirates from asthmatics without these characteristics. In only one asthmatic was there suggestion that overt infection of the lower respiratory tract contributed to exacerbation of asthma. These results do not lend support to the empiric use of antibiotics in the management of unexplained asthmatic relapse.