To determine whether tampons composed of cotton or rayon differ in their effects on production of TSST-1 in vitro, two methods of bacterial cultivation, with and without agitation, were used to study the effects of 16 commercially available and experimental tampons on production of TSST-1. Experiments were done in blinded fashion. TSST-1 was produced in medium alone in the absence of a tampon by both methods. Neither cotton nor rayon tampons consistently increased toxin production, nor were there significant differences between them in their effects on TSST-1. In contrast, a tampon composed of carboxymethylcellulose and polyester foam increased production of TSST-1 to a large degree in both culture systems. Thus, neither cotton nor rayon amplifies production of TSST-1 in vitro, and cotton tampons cannot be claimed to be inherently safer on the basis of such data.