Traditional models of physical dependence suggest that nicotine dependence should be reflected by the extent of drug exposure (e.g., smoking rate) and by evidence of physiological adaptation (e.g., withdrawal severity). An affective model suggests that nicotine dependence should be related to an individual's tendency to experience negative affect and expectations that nicotine use would ameliorate such affect. This research investigated the ability of these 2 models to predict relapse back to smoking at 6 months postquit. Logistic regression models were developed and tested in 505 heavy smokers participating in nicotine patch clinical trials. Results supported both models, but the most potent predictor of outcome was postquit negative affect, which accounted for much of the predictive validity of traditional measures of nicotine dependence. Affective reactivity appears to be a core constituent of dependence.