Most smokers relapse following smoking cessation treatment. More effective smoking cessation therapies are needed to prevent the high rates of relapse. Selegiline is a selective inhibitor of monoamine oxidase B (MAO B) and has been used clinically in combination with levodopa to treat Parkinson's disease. Selegiline permits the stabilization of dopamine (DA) levels in the brain by preventing the rapid degradation of DA by means of MAO B and is used as an adjunct to levodopa therapy causing a dose-sparing effect and enhancing dopaminergic transmission. Selegiline's effect on MAO B and the resulting effect on brain DA has interesting implications for the treatment of nicotine dependence because brain DA systems may play a key role in the mediation of reward learning behavior. Previous research suggests that the brains of living smokers show a 40% decrease in the level of MAO B relative to nonsmokers or former smokers. The purpose of this study is examine whether selegiline, administered in the form of a skin patch, is effective for smoking cessation.