Preparations of cell wall and protoplasm were made from young Bordetella pertussis cells and tested for: a) their ability to immunize mice against fatal B. pertussis infection, b) their ability to sensitize mice to histamine, and c) their toxic properties. It was found that the heat labile toxin was mainly present in the protoplasm whereas the protecting antigen and the histamine sensitizing factor were located principally in the cell wall.