The purpose of this study is to better characterize differences in mood, attention, brain activation patterns underlying the beneficial effects of pharmacological treatments previously demonstrated to be help individuals successfully quit tobacco smoking. Smokers will be randomly assigned to one of three treatments: 1) bupropion sustained release (SR), 2) nicotine patch, or 3) placebo patches plus pills across a 45-day period with a 3-week intensive post-treatment follow-up. In addition, 20 percent of the subjects will be randomized to a delayed-quit control group.