Subjective stress is a well-documented predictor of early smoking relapse, yet our understanding of stress and tobacco use is limited by the reliability of current available measures of stress. Functional magnetic reasoning imaging (fMRI) could provide a much-needed objective measure of stress reactivity. The goal of this dissertation is to contribute to the understanding of abstinence-induced changes in stress reactivity by examining neural, neuroendocrine (cortisol), and subjective measures of stress response during abstinence. In addition, this study investigated the influence of individual variation in nicotine metabolism rates on these measures of stress reactivity. Seventy-five treatment-seeking smokers underwent blood oxygen level dependent (BOLD) fMRI during the Montreal Imaging Stress Task (MIST) on two occasions: once during smoking satiety and once following biochemically confirmed 24-hour abstinence (order counter-balanced). The primary outcome measure was brain response during stress (vs. control) blocks of the MIST. Neural stress reactivity during abstinence (vs. satiety) was associated with significantly increased activation in the left inferior frontal gyrus (IFG), a brain region previously associated with inhibitory control. Greater abstinence-induced change in brain response to stress was associated with greater abstinence-induced change in subjective stress. However, there was no association with abstinence-induced change in cortisol response. In addition, higher rates of nicotine metabolism were associated with increased abstinence-induced change in self-reported stress, but not with brain or cortisol response. This study provides novel evidence that the brain response to stress is altered during the first 24 hours of a quit attempt compared to smoking satiety. These results underscore the importance of stress response during abstinence, and suggest that neuroimaging may provide a useful biomarker of stress response during the early smoking cessation, a period when smokers are most vulnerable to relapse.