In the context of adolescent smoking adoption, this study examined the presumed influence hypothesis, a theoretical model suggesting that smoking-related media content may have a significant indirect influence on adolescent smoking via its effect on perceived peer norms. That is, adolescents may assume that smoking-related messages in the mass media will influence the attitudes and behaviors of their peers and these perceptions in turn can influence adolescents’ own smoking behaviors. Analyzing data from a sample of 818 middle school students, we found that both pro- and antismoking messages indirectly influenced smoking susceptibility through their perceived effect on peers. However, this indirect effect was significantly stronger for prosmoking messages than for antismoking messages, an outcome that most likely increases adolescents’ susceptibility to cigarettes. doi:10.1111/j.1460-2466.2006.00002.x People who perceive that mass media can powerfully influence others may, often quite sensibly, react to that perception themselves. These reactions to presumed influence on others fall into two general categories. One category is prevention: Assuming, for example, that sexual content in media will corrupt the morals of others, people may support censorship of such content in an effort to thwart the undesirable outcome. The other reaction is accommodation: Assuming, in this alternative scenario, that advertising is going to influence public opinion about what is fashionable and attractive, people may adopt these new fashions themselves. In both cases, regardless of any actual direct effect, media may be exerting a very real indirect effect on individuals—an indirect effect via presumed influence on others. This general indirect effects model has been called the presumed influence hypothesis (Gunther & Storey, 2003). Prevention reactions have been repeatedly documented over the past 10 years, largely in the context of third-person-effect research (see, e.g., Gunther, 1995;