The efficacy of penicillin administered parenterally in the treatment of many types of bacterial pneumonia is well established. Likewise, aureomycin, chloramphenicol, and oral penicillin have been successfully employed in this disease. Unfortunately, the wide therapeutic range of these agents has resulted in a failure in most instances, both in home and hospital practice, to do careful diagnostic studies. Usually, the necessary laboratory work is reserved for cases failing to respond to therapy. For this reason, accurate figures dealing with the treatment of large groups of pneumonia patients are becoming increasingly difficult to assemble, and, as a consequence, data regarding the use of the newer antibiotics are limited. Hence, confusion exists in the minds of many as to the antibiotic of choice in the initial treatment of bacterial pneumonia. Of considerable interest, therefore, are data collected in a single hospital where these antibiotics have been employed during the same pneumonia season.