2. Reinstillation of fluid (broth, physiological salt solution) into the respiratory passages of mice several days after sublethal viral infection converts the viral infection into a lethal one.

3. Sulfonamide chemotherapy controls the bacterial component of combined bacterial and viral infection of mice, produced by intrabronchial inoculation of mixtures of bacteria and sublethal or lethal doses of virus.

4. Bacterial pneumonia may be superimposed upon sublethal viral infection in mice by inhalation of fine droplets of bacterial suspension several days after inoculation of virus. Normal mice inhaling fine droplets of bacterial suspension fail to develop obvious disease.

5. Sulfonamide chemotheiapy controls bacterial pneumonia superimposed on sublethal viral infection by inhalation of fine droplets of bacterial culture.

6. The secondary bacterial penumonia does not convert the sublethal viral infection into a lethal one.

7. If another pandemic of influenza occurs, it is probable that sulfonamide chemotherapy will be valuable in the treatment of secondary bacterial pneumonia and will be effective in lowering the case fatality rate if the viral component of the infection is not severe enough by itself to cause death.