Physical and chemical factors that may affect the growth of strains of Staphylococcus aureus that are associated with toxic-shock syndrome were examined for their effect on expression of pyrogenic exotoxin type C (PE-C). Significantly more PE-C was made when cultures were incubated at 37 C rather than at 30 C, although bacterial growth was similar at the two temperatures. Furthermore, 32-fold more toxin was made aerobically versus anaerobically for the seven strains tested, whereas only a twofold difference in bacterial growth was seen. Maximal toxin production occurred at pH 7 and pH 8, although the strains grew well in the range of pH 6 to pH 8. Glucose had little effect on growth and toxin production at levels from 0 to 0.3% but suppressed bacterial growth and, more extensively, toxin production at a level of 3%. Significant amounts of PE-C were made in beef-heart medium, brain-heart infusion broth, and Todd-Hewitt broth, but lesser amounts were made in trypticase soy broth.