In a controlled blind study sputum of 84 patients suffering from chronic bronchitis was bacteriologically examined prior to treatment. Hereby resistance against azidocillin was exhibited by six of the pathogenic agents or the suspected ones; the bacteria in 18 samples of sputum showed resistance against co-trimoxazol. Azidocillin demonstrated, as opposed to co-trimoxazol, slight yet not significant advantages in the elimination of the agents. Azidocillin was, however, significantly superior to co-trimoxazol in the physicians total assessment, which included the clinical process as well as the components of the sputum. According to the results of our investigations, the treatment of chronic bronchitis can be started without examining the sputum. However, in patients showing exacerbation of chronic bronchitis with life-threatening complications, the sputum should be examined before medication is conducted. In such cases we recommend the treatment to be started immediately with an appropriate bactericide like azidocillin and to be continued till the result of the antibiogram is finally established.