1. Highly purified scarlet fever toxin has been prepared from culture filtrates of two scarlatinal strains (NY5 and 594B) of hemolytic streptococcus grown on a medium of defined composition.
2. The flocculation reaction of Rane and Wyman has been studied quantitatively and has been shown specific for scarlet fever toxin and antitoxin.
3. Scarlet fever toxin from strains NY5 and 594B are quantitatively identical in their immunological behavior.
4. Pure scarlet fever toxin contains 0.00023 mg. nitrogen per flocculating unit and close to 1.3 x 108 skin test doses per mg. nitrogen as calculated from the immunological data. Both the immunological and the analytical data suggest that scarlet fever toxin is a protein. Similar calculations indicate that scarlet fever antitoxin contains 0.00093 mg. nitrogen per unit.
5. The scarlet fever toxin-antitoxin complex is readily dissociated in dilute solutions. In this respect the scarlet fever toxin-antitoxin system contrasts sharply with the diphtheria toxin-antitoxin system.
6. The scarlet fever toxin-antitoxin reaction is discussed in relation to other flocculation reactions.