The influence of depressive symptoms on smoking cessation was examined among 600 African American smokers who participated in a randomized, placebo-controlled trial of sustained-release bupropion hydrochloride. Depressive symptoms were assessed at baseline, at week 6 (end of treatment), and at 6-month follow-up. The study examined three separate questions: (a) Whether depressive symptom levels were related to smoking cessation, (b) whether bupropion was more effective for smokers who had higher depressive symptoms at baseline (i.e., a moderator model), and (c) whether changes in depressive symptoms would account for the efficacy of bupropion for smoking cessation (i.e., a mediator model). Depressive symptoms at baseline were not predictive of cessation; however, increases in depressive symptoms from baseline predicted reduced cessation at the end of treatment, and higher depressive symptoms at week 6 and month 6 were associated with a reduced likelihood of smoking cessation at those time points. The moderator model was not supported, but the mediation analyses indicated that alleviation of depressive symptoms partly accounted for bupropion-assisted smoking cessation at end of treatment. Results extend prior findings to African American smokers and suggest that clinicians consider increases in depressive symptoms after quitting rather than baseline depressive symptoms in predicting risk of treatment failure. Results also suggest that even though bupropion may facilitate cessation in part by reducing depressive symptoms, it appears to be no more effective for more depressed smokers, and that mechanisms other than depressive symptom alleviation account for most of its efficacy.