Objective: An experimental study tested the effects of positive and negative mood on the processing and acceptance of health recommendations about smoking in an online experiment. It was hypothesised that positive mood would provide smokers with the resources to systematically process self-relevant health recommendations.Design: One hundred and twenty-seven participants (smokers and non-smokers) read a message in which a quit smoking programme was recommended. Participants were randomly assigned to one of four conditions: positive versus negative mood, and strong versus weak arguments for the recommended action.Main outcome measures: Systematic message processing was inferred when participants were able to distinguish between high- and low-quality arguments, and by congruence between attitudes and behavioural intentions. Persuasion was measured by participant's attitudes towards smoking and the recommended action, and by their intentions to follow the action recommendation.Results: As predicted, smokers systematically processed the health message only under positive mood conditions; non-smokers systematically processed the health message only under negative mood conditions. Moreover, smokers' attitudes towards the health message predicted intentions to quit smoking only under positive mood conditions.Conclusion: Findings suggest that positive mood may decrease defensive processing of self-relevant health information. © 2012 Copyright Taylor and Francis Group, LLC.