Specimens of sputum from 17 patients with pneumonia at Camp Gruber, Okla., have been examined for the presence of an infectious agent which might have caused the illnesses. Most of the sputums were obtained three to four weeks after the onset of the disease, but many of the patients were still febrile at the time of collection. In addition, sputums were collected from 8 patients not involved in this outbreak of pneumonia for the purpose of comparison. Several samples of dust from a storm cellar, incriminated epidemiologically as a probable source of the infection, and of dirt from a nearby machine gun emplacement were also collected for study. Cultures, inoculation of animals and serologic tests were carried out. Particular emphasis was placed on mycologic examinations, because of the clinical characteristics of the disease. EXPERIMENTAL DATA Cultures for Bacteria. —Cultures for bacteria in the sputums were made on blood agar plates.