1. Plasmas from guinea pigs, chronically infected with group C hemolytic streptococci, neutralize the components of bacterial extract which exert a marked toxic action on hypersensitive cells in vitro.
2. The neutralizing capacity of these immune plasmas is relatively specific for the bacterial extract, and is not due to a variable nonspecific effect on normal or hypersensitive tissue cells.
3. A rough correlation between the agglutinin titer and the relative neutralizing capacity of immune plasma suggests that the latter may be a manifestation of antibody action.
4. The tolerance by guinea pigs of chronic hemolytic streptococcal lymphadenitis is explainable, at least in part, by the neutralizing capacity of their plasmas, since such soluble bacterial products as may be absorbed from infectious foci would probably be neutralized before they could exert a deleterious influence on the hypersensitive cells of the animals.