A study was undertaken to evaluate the production of enterotoxin B (Ent B), EntC1, and toxic shock syndrome toxin 1 (TSST-1) by isolates of Staphylococcus aureus from patients with toxic shock syndrome (TSS) and from a variety of other sources. Levels of toxin in culture supernatants were measured by a quantitative immunodiffusion assay. Most vaginal TSS isolates produced TSST-1, either alone or with EntC1. However, strains that produced EntB or EntC1 but did not express TSST-1 were commonly isolated from patients with nonmenstrual TSS; EntB was usually produced alone or--rarely--with EntC1. These results were confirmed by probing DNA from representative isolates with an internal probe of the EntC1 gene (entC1). Extensive sequence homology between entC1 and entB enabled detection of both genes under conditions of high stringency. The genomic location of entC1 in strains producing both EntC1 and TSST-1 varied little but was dependent on the mammalian host. In contrast, the genomic location of entC1 or entB in strains producing EntC1 or EntB alone was variable. These results suggest that these genes are contained on mobile elements.