1. Type-specific agglutination of Pneumococcus Types I, II and III has been demonstrated in antisera largely deprived of the carbohydrate antibody.
2. The type-specific agglutinogens in Pneumococcus I and II responsible for agglutination in such antisera are inactivated by heating in alkaline solution at 100°C. The specific carbohydrate remains unaltered under these conditions.
3. The relationship of the type-specific agglutinogen in Pneurmococcus I to the type-specific A substance has been discussed.
4. The possible application of these results to the standardization of therapeutic antisera by agglutinin titre has been discussed.
5. On the basis of the experiments recorded a tentative explanation is offered for the failure of Pneumococcus Type II to absorb the agglutinins from anti-B. friedlaenderi Type B serum.