For many years, mass media health campaigns have strived to change population health-related attitudes and intentions. While it is important to assess the direct effects of exposure to health campaign messages on these campaign outcomes, it is equally valuable to examine whether messages can be further propagated into the public communication environment. When people decide to replicate (replication) the core arguments used in campaign messages as they diffuse them to additional campaign targets, this enhances the reach of a campaign. Moreover, when people extend (extension) the core arguments of campaign messages by diffusing arguments in the same category as the campaign theme but those not specifically targeted in campaign messages, this increases the diversity of campaign-relevant communication. This dissertation aimed to examine how exposure to anti-smoking campaign messages influences patterns of replication and extension with four experimental studies. The first two studies examined whether message exposure can lead to replication and extension. Then, guided by construal level theory, the latter two studies examined whether different message characteristics and mindsets can increase or decrease patterns of extension. Study 1 found that exposure to why appeal messages (messages about reasons to quit smoking) and how appeal messages (messages about methods to quit smoking) influenced people to choose arguments that were targeted by the messages they were exposed to, to send to smokers. Study 2 focused on whether exposure to these messages influenced the selection of arguments that were consistent with the appeals (why and how), but were not targeted by the messages participants were exposed to, and found partial support. Study 3 found that exposure to why appeal messages with proximal temporal frames could hinder the selection of non-targeted why arguments. However, no support was found for the hypothesis that inducing different construal mindsets could increase or decrease the selection of non-targeted arguments (Study 4). The studies provided empirical tests of replication and extension—both outcomes that are important for advancing campaign effects. They also delved into the research question of whether certain message characteristics can promote or undermine the pattern of extension. Study results can inform campaign developers about which message strategies could be successful in further propagating campaign-relevant information into the public communication environment.