AbstractSeveral bacteria, such as staphylococci and streptococci, can produce superantigens (SA) that induce the activation of T cells in humans. Although these organisms are the major causes of infection in children, the evidence that T cells are vigorously activated by SA produced by such organisms has not been reported except for toxic shock syndrome. In a previous paper, we demonstrated that inhibitory IgG antibodies (Ab) to SA in humans may protect against SA stimulation. In the present study, we investigated the occurrence of these inhibitory Ab to SA in 94 healthy children by the enzyme linked immunosorbent assay technique and the suppressive effect on T cell stimulation by SA.The positivity of Ab to streptococcal pyrogenic exotoxin (SPE)‐A, SPE‐C and staphylococcal enterotoxin B (SEB) increased with age. The age at which more than 50% of children exhibited Ab to SA was 1 year for SEB, 6 years for SPE‐C and 11 years for SPE‐A. Sera from these children were inhibitory to T cell proliferation elicited by SA in proportion to the concentration of IgG Ab to each SA. Sera supplemented with IgG Ab to SA by gamma‐globulin therapy became inhibitory to T cell proliferation by SA. We conclude that, as children grow, they can develop Ab to SA that may play a role in protecting them against vigorous T cell activat