The aim of the proposed work is to extend the classification of the alpha and nonhemolytic streptococci of the human respiratory tract by the use of immunologic biochemical and genetic techniques in order to determine, if possible, whether or not certain of those organisms play a more prominent role than others in chronic disease of the lower respiratory tract. Investigations will be concerned with the definition of the capsular and cell wall antigens of these organisms, some of which cross react with analogous antigens of pneumococcus, with especial emphasis upon strains isolated from the lower respiratory tract by transtracheal puncture.