Staphylococcal enterotoxins represent a group of proteins, which are secreted by Staphylococcus aureus and cause the intoxication staphylococcal food poisoning syndrome. The illness characterised by high fever, hypotension, diarrhea, shock, and in some cases death. Their molecular masses range between 27 and 30kD. At present, seven enterotoxins are known, namely A, B, C1, C2, C3, D and E. Their aa sequences have been determined and it was shown that all are single chain polypeptides containing one disulfide bond formed by two half cystines located in the middle of the polypeptide chain, which form the so called cysteine loop. Enterotoxins are extremely potent activator of T cells, stimulating the production and secretion of various cytokines which mediate many of the toxic effects of these substances. Enterotoxins are Superantigens, inducing polyclonal T cell activation by binding to the TCR and to the alpha chain of the MHC II molecule simultaneously.