Atypical pneumonia has been reported as occurring in various Army and Navy organizations, as well as in civilian institutions in the United States, during the last few years. It is probably an old disease, endemic in some localities, assuming epidemic character due either to change in the virulence of the causative agent or an increase in individual susceptibility. The diagnosis is made from the history, physical examination, evaluation of laboratory findings, as smears from sputum or throat washings, animal inoculations and blood cultures, and roentgen examination. The clinical course of atypical pneumonia, possibly of virus origin (1–3), differs somewhat from that of bacterial pneumonias, in that the patient with atypical, non-bacterial pneumonia is not so ill. No one to date has been able to isolate a causative agent of atypical pneumonia of non-bacterial origin to be found in the majority of cases. It is believed by some workers, however, that parrot fever, ornithosis, or psittacosis is related closely to the disease, if not the direct cause in some instances (4). It seems unlikely that the psittacine virus could be the direct cause of all atypical, non-bacterial pneumonias, as usually the patients with psittacosis are decidedly more ill than the average patient with atypical pneumonia of non-bacterial origin. The onset in the non-bacterial type of pneumonia is often insidious, with mild coryza and a watery nasal secretion which soon becomes tenacious and at times blood-streaked but not grossly bloody. There is an annoying cough, possibly with substernal pain and malaise, but seldom are there enlarged cervical nodes. The temperature is usually elevated; it may reach 102 or 103° F. but rarely 104° or 105° F. In our series of 91 cases there were 2 with a temperature of 106° F. and 6 reaching 105° F. The temperature dropped by lysis, as a rule, in five to twenty days after the onset of the disease. In this series the majority of patients were fever-free ten days after entering the hospital. Seldom did the temperature fall below 98°. It has been observed by some that in atypical, non-bacterial pneumonia the temperature often drops about the third day. This finding was not particularly in evidence in our series except where it was believed to be due to the effect of one of the sulfa drugs, administered during the preceding twenty-four or forty-eight hours, on secondary bacterial invaders. There was slight, if any, elevation of the pulse or respiratory rate. Rarely did the pulse rate exceed 100. In the majority of cases it was seldom over 80 per minute; in a few it ranged from 80 to 90 per minute. If considerable consolidation developed, the pulse was likely to be rapid. The average respiratory rate was 20 per minute. In a moderate number of patients the rate was from 20 to 30 per minute. In few was it as high as 40 per minute.