A method and apparatus for analyzing pulmonary function including diffusing capacity and cardiac output or local pulmonary blood flow while necessarily determining alveolar volume in order to complete the above-noted analysis. In order to provide a rapid response in each of the abovenoted analyses or determinations, appropriate gases are caused to be inhaled and exhaled through a sample cell wherein a percentage of each gas may be constantly monitored during inhalation and exhalation by means of non-dispersive infrared absorption techniques, the sample cell and associated components of the pulmonary function analyzing device including additional features to facilitate the abovenoted analyses and determinations, the combination of gases employed for monitoring the pulmonary functions being selected to permit accurate detection by infrared absorption techniques.