Staphylococcal enterotoxins and streptococcal pyrogenic exotoxins constitute a family of biologically and structurally related toxins produced by Staphylococcus aureus and Streptococcus pyogenes [1,2]. These toxins share the ability to bind to the major histocompatibility complex proteins of their hosts. The toxins that belong to this family are:

• Staphylococcal enterotoxins are the cause of staphylococcal food poisoning syndrome. The sequence of six different enterotoxins is known: SEA, SEB, SEC1, SEC3, SED, and SEE.
• Streptococcal pyrogenic exotoxins are the causative agents of the symptoms associated with scarlet fever. The sequence of two pyrogenic exotoxins is known: SPEA, and SPEC.
• Staphylococcus aureus toxic shock syndrome toxin-1 (TSST-1).

While the enterotoxins and the pyrogenic exotoxins are closely related, TSST-1 seems to be only distantly related to the other toxins. We developed two patterns for this family of toxins. The first one is based on a well conserved region of enterotoxins and pyrogenic exotoxins, but which does not pick up TSST-1; the second pattern is derived from a more diffuse region of similarity common to all these toxins.