The staphylococcal enterotoxins have been termed superantigens based on their ability to stimulate polyclonal proliferative responses of murine and human T lymphocytes expressing particular T-cell receptor V beta gene products. Certain of these toxins have been shown both to activate and to induce anergy in reactive T cells. Staphylococcal enterotoxin B is known to interact with murine T cells bearing V beta 3, -7, -8.1, -8.2, -8.3, and -17. In BALB/c mice V beta 3+ and V beta 17+ T cells are deleted; V beta 7+ T cells are low in frequency. BALB/c mice sensitized to ovalbumin via the skin and airways develop immediate hypersensitivity including IgE/IgG1 antiovalbumin antibodies, immediate cutaneous reactivity to ovalbumin and, increased airway responsiveness. In both in vitro and in vivo studies, the development of these responses has been associated with the V beta 8+ subset of T cells and controlled by V beta 2 + T cells. In view of the central role of V beta 8+ T cells in these responses, we tested the effects of staphylococcal enterotoxin B on the development of immediate hypersensitivity in this system. Intradermal injection of staphylococcal enterotoxin B prevented the development of these responses in the absence of a major deletion of V beta 8+ T cells. The data suggest that the administration of staphylococcal enterotoxin B prevented the antigen-induced expansion of V beta 8+ T cells resulting in a state of responsiveness or anergy, thus preventing the manifestations of immediate hypersensitivity. Bacterial toxins may provide a novel approach to intervention in allergic or autoimmune diseases.