An apparatus is described for the partitioning of exhaled air into seven separate fractions beginning with the earliest portion of upper respiratory air and continuing to the terminal fraction of deep‐lung air. The same volumetric fractions from successive exhalations are collected over a test period of any practical duration. This apparatus has been employed for the study of lung retention of inhaled particulate matter with particular reference to the separate estimate of upper respiratory retention and penetration to and deposition of particulate matter in alveolar spaces. The apparatus is employed with a mechanical respirator of the Drinker type, which fixes the respiratory pattern at any desired frequency and tidal volume.