Conversation about health messages and campaigns is common, and message-related conversations are increasingly recognized as a consequential factor in shaping message effects. The evidence base is limited, however, about the conditions under which conversation may help or hinder health communication efforts. In this study, college students (N = 301) first watched a short sleep video and were randomly assigned to either talk with a partner in an online chat conversation or proceed directly to a short survey. Unknown to participants, the chat partner was a confederate coached to say positive things about sleep and the message ('positive' chat condition), negative things ('negative' chat condition), or unrelated things ('natural' chat condition). All respondents completed a short survey on beliefs about sleep, reactions to the message, and intentions to get adequate sleep. Respondents had greater intentions to engage in healthy sleep when they engaged in positive conversation following message exposure than when they engaged in negative conversation after the message (p < 0.001). Positive emotion experienced in response to the message and positive chat perceptions were significant predictors (p < 0.05) of intentions to achieve healthy sleep. Health message designers may benefit from understanding how messages are exchanged in peer-to-peer conversation to better predict and explain their effects.