We found that when group A streptococci are cocultured with human pharyngeal cells, they upregulate and secrete a 25-kDa toxin, determined to be the bacteriophage-encoded streptococcal pyrogenic exotoxin C (SpeC). This prompted us to determine if the bacteriophage themselves are induced during coculture conditions. We found that bacteriophage induction does occur, resulting in the release of approximately 10(5) phage particles during the 3-h coculture. Furthermore, we show that the bacteriophage induction event is mediated by a pharyngeal cell soluble factor for which we provide an initial characterization.