Summary A specific precipitate band obtained by the gel diffusion technique has been identified as the enterotoxin-antienterotoxin band. A monovalent serum specific for enterotoxin produced by staphylococcus strain S-6 was prepared. Highly potent enterotoxin from thirteen food poisoning stains of Staphylococcus cross reacted with this serum; whereas the enterotoxin from another strain, 196E, did not cross react. The equivalence ratio for enterotoxin calculated by the Oudin technique was 2–3 times the equivalence ratio determined from neutralization studies with enterotoxin given orally to monkeys.