In-vitro studies were done to investigate the role of tampons and Staphylococcus aureus in toxic shock syndrome. Tampons did not enhance the growth of S. aureus in nutrient broth or human blood. Intrinsic contamination of tampons with S. aureus was not found among the 504 tampons cultured (95% confidence limits of fraction contaminated; 0 to 0.007). Toxin-producing S. aureus persisted significantly longer on artificially contaminated Rely tampons (Procter & Gamble) than on the other brands tested. The proportion of clinical isolates of S. aureus capable of producing toxin increased from two of 36 in 1960 to eight of 20 in 1979 (p = 0.002, Fisher's exact test). This general increase in the proportion of toxin-producing strains may partially explain the increase in cases of toxic shock syndrome in recent years.