Exogenous antigens are presented to T lymphocytes through mechanisms that ensure high recognition specificity. Recently described superantigens in contrast to conventional antigens are particles that follow a different processing and presentation route not binding to a specific region of T lymphocyte receptors. These particles bind to a large number of T lymphocytes, generating a disproportionate and non-specific immune response. Two types of superantigens have been described. Endogenous superantigens, transported in the host genoma, have been involved in clonal depletion and immunological tolerance phenomena. Exogenous superantigens, mainly bacterial toxins, have been involved in several diseases. There is evidence that these antigens participate in diseases such as Kawasaki disease, toxic shock caused by Staphylococcus aureus, rheumatoid arthritis, HIV infection and Streptococcus pyogenes infections.