The anatomical distribution of plasma cells and other cells containing immunoglobulin in the respiratory tract, and the relative proportions of the immunoglobulin classes have been estimated on necropsy tissues from nine adult human subjects without respiratory disease and eleven subjects suffering from chronic bronchitis. Cell counts on multiple sections stained by immunofluorescent methods for the presence of immunoglobulin were carried out on upper trachea, main bronchus and lower lobe bronchus, and the general appearances in peripheral lung were noted.