Summary: Staphylococcal enterotoxin may be detected by the intra-abdominal injection into kittens of filtrates whose α- and β-toxins have been destroyed by heat or formalinization, or have been removed by preliminary absorption with serum containing antibodies to the α- and β-toxins but not to the enterotoxin. The enterotoxin has definite and specific antigenic properties. The sera of animals immunized with filtrates containing enterotoxin develop neutralizing properties against this antigen. A specific flocculation reaction, apparently involving the enterotoxin and its antibody, is described. Methods are given whereby the flocculation zone, representing the optimal ratios for neutralization of the enterotoxin in a filtrate by its corresponding antibody, may be distinguished from other flocculation zones due to α- and β-toxin-antitoxin reactions.