Staphylococcus aureus carriers have high-titer serum antibodies against non-enterotoxin gene cluster (egc) superantigens, whereas they lack anti-egc antibodies, suggesting different superantigen expression profiles in vivo. We measured the superantigen transcripts in S. aureus directly isolated from the nose of persistent carriers and correlated them with the superantigen-neutralizing antibody response. While neutralizing serum antibodies against the staphylococcal enterotoxins A and C (SEA and SEC) were found in carriers, antibodies against the egc-encoded staphylococcal enterotoxin-like toxin O (SElO) were rare. Surprisingly, the transcription of selo was comparable to sea and sec during nasal colonization. Thus, egc superantigens are transcribed during nasal colonization, but this is not sufficient to induce a serum antibody response.