A comparative study was undertaken in order to ascertain the effects of a Mycoplasma pneumoniae infection on pulmonary function. It appears that the literature has many articles devoted to the clinical symptomatology of this type of infection but there is very little information available on the abnormalities which occur in the lungs with this infection. The patients who were used as a comparative model had lung lesions which gave a similar radiographic appearance. The significant finding was that an obstructive syndrome with increased airway resistance was noted in the M.pneumoniae pneumonia patients.