OBJECTIVE. The aim of this study was to investigate the effects of bupropion sustained release (SR) on cognitive function, evaluated by event-related potentials (ERPs), in heavy tobacco smokers. MATERIAL AND METHODS. A total of 10 healthy volunteers (6 men and 4 women) were enrolled into the study. P3a and P3b components were evaluated by the novelty P3 paradigm. The ERP recordings were taken after the overnight abstaining and the first dose on the 1st day, on the 7th day, and 45th day of the therapy. RESULTS. The analysis of electrophysiological data in response to the standard stimuli in the parietal area after 7-day bupropion SR treatment revealed a significant increase in the P2 latency (P<0.05). With respect to the drug use × topography effect, an increasing trend of borderline significance in the P3b and P2 amplitudes against target events in the parietal area was observed (P=0.08 for both). A significant increase in the P3a amplitude in the parietocentral area was also observed on the seventh day of treatment (P<0.05). CONCLUSIONS. The reduction of P3a in the frontal area may be due to the decreased distractibility of task-irrelevant novel events, which may mean an augmentation of focused attention to task-relevant target events. The increases in the P3b and P2 amplitudes for target events in the parietal area are very suggestive of this hypothesis, since these components reflect the response to task-relevant target events. Meanwhile, the increased P2 latency for standard events may reflect reduced attention resources for the processing of standard events due to increased attention resources allocated for task-relevant target events. Decreased distractibility and increased attention are believed to be caused by bupropion.