Current smoking cessation pharmacotherapy paradigms ignore the over-learned behaviour associated with smoking, thus contributing to the relatively poor absolute efficacy of pharmacotherapy. Chronic nicotine use causes adaptive changes in the brain that differ from the acute effects leading to craving when smoking is stopped. This is a key element of relapse. Thus, the development of more effective treatments involves a better understanding of craving and relapse by exploring the interaction between the psychology and neurobiology of nicotine addiction. Bupropion, an amphetamine derivative, has demonstrated efficacy in smoking cessation in motivated smokers. Its' mechanism of action is unclear but may be mediated by extinction processes. We hypothesize that bupropion will reduce cue-responsiveness and subsequent cravings in current smokers who are not consciously attempting to quit or cut down on smoking. Fifty smokers (>10 cigarettes/day) of either sex will be recruited to take either oral placebo or bupropion 150 mg twice daily for a total of 42 days. Subjects will attend bi-weekly experimental sessions where cue-responsiveness will be measured using physiological and subjective responses to a variety of neutral and smoking-related cues. Subjective effects will be measured using the Questionnaire of Smoking Urges, the Tobacco Craving Questionnaire and Visual Analog Scales. Subjects will record smoking behaviour and subjective experiences daily in a smoking diary. Outcome variables include cue responsiveness, daily diary ratings, exhaled end tidal CO levels, plasma cotinine levels, and subjective effects. Gender effects will be assessed by using sex as a covariate in the analysis. This study will provide preliminary data on pharmacotherapy-assisted extinction as a novel approach to smoking cessation.