Following the demonstration of an exotoxin by the Dicks1from strains of hemolytic streptococci isolated from scarlet fever, Parker2reported similar toxic substances in sterile filtrates of certain strains ofStaphylococcus aureus. In her work the skin reactions were observed in rabbits. These reactions were neutralized by the serums of rabbits immunized intradermally with the exotoxin. In our work of testing the staphylococcus filtrates we employed the methods that were used on man by the Dicks1with streptococcus toxin. Freshly isolated strains ofStaphylococcus aureuswere obtained from various lesions, such as furuncles, carbuncles, abscesses of the breast and kidney, and from fatal cases of staphylococcus septic pyemia. They produced typical pigment, and on blood agar 50 per cent of the strains caused hemolysis. Both hemolytic and nonhemolytic strains produced potent toxins in the filtrates. All strains tested yielded exotoxin, which, however, varied considerably in potency. The