1. Pneumococci of Type I and Type II are responsible for the majority of the cases of lobar pneumonia. 2. Among the pneumococci found in the mouths of healthy individuals, Type IV predominates, Type III is fairly frequent, and atypical organisms of Type II are occasionally encountered. Organisms of these types give rise to a minority of cases of lobar pneumonia. 3. Healthy persons intimately associated with cases of lobar pneumonia may harbor in their mouth secretions the highly parasitic pneumococci of Types I and II. 4. Occasionally a carrier of Type I or Type II pneumococcus is encountered in whom it is impossible to trace any contact with an infected patient. 5. Convalescents from lobar pneumonia may carry for a considerable period of time the type of pneumococcus with which they were infected.