This study was made on 163 pneumonia cases, 73 in children and 90 in adults. The conclusions are: (1) Fixed type pneumococci cause a large proportion of the cases of lobar pneumonia in childhood, and are uncommon in cases of broncho-pneumonia during this period. (2) Pneumonia due to Types I and III pneumococci has a much lower mortality in children than in adults. (3) Heavy blood stream invasion in children with pneumococcus pneumonia is rare. (4) Protective bodies appear in children with pneumococcus pneumonia, as in adults, about the time of recovery. Type specific agglutinins similarly appear in children, but their appearance is less frequent than in adults, and apparently less frequent in younger than in older children. (5) The marked pneumococcemia seen in fatal cases of lobar pneumonia in adult man suggests a special reactivity on his part towards the pneumococcus different from that of the child.