Ecological momentary assessment was used to examine immediate changes in 87 college students’ smoking-related attitudes, beliefs, and intentions as a joint function of their exposure to antismoking media and smoking status. Students (37 never smokers, 41 experimental smokers, and 9 current intermittent smokers) carried handheld data-collection devices for 3 weeks to record naturally occurring exposures to antismoking media and respond to investigator-initiated control prompts. At each reported exposure to antismoking media and each control prompt, participants reported their smoking-related attitudes, perceptions of the prevalence of smoking among their peers, resistance self-efficacy, and intentions to smoke. Mixed-effects regression was used to compare responses between encounters with antismoking media and control prompts. Experimental smokers reported weaker intentions to smoke and greater resistance self-efficacy at moments of exposure to antismoking media than at control prompts. Regardless of smoking experience, participants reported higher perceived prevalence of smoking at times of exposure to antismoking media than at control prompts. These findings generally support the value of antismoking media messages for shifting the beliefs and intentions of experimental smokers, who are at high risk for becoming committed regular smokers.