BackgroundSocial interactions are a key mechanism through which health communication campaigns influence behavior. Little research has examined how conversations about pictorial warnings motivate behavior. PurposeWe sought to establish whether and how smokers' conversations explain the effect of pictorial warnings on quit attempts. MethodsUS adult smokers (n = 2149) participated in a controlled trial that randomly assigned them to have their cigarette packs labeled with pictorial or text-only warnings for four weeks. Surveys assessed the number of conversations sparked by pictorial warnings and the theoretical mechanisms cognitive elaboration and social norms at each visit. Analyses used structural equation modeling to test our theorized mediation models. ResultsThe number of conversations about the warnings mediated the relationship between exposure to pictorial warnings and quit attempts (p < .001). In serial mediation analysis examining possible theoretical mechanisms, the number of conversations was associated with greater cognitive elaboration, which in turn was associated with being more likely to make a quit attempt (p < .05). Social norms did not explain the influence of conversations on quit attempts. ConclusionsPictorial warnings increased conversations about the warnings, which led to greater cognitive elaboration, which led to greater quit attempts. Our findings suggest designing warnings that increase conversations in order to better inform and motivate smokers. Furthermore, these findings improve our understanding of why conversations matter in health communication.