It has been reported that nicotine shows some beneficial effects on Parkinson's disease. The purpose of the present study is to assess the therapeutic effects of nicotine chewing gum in patients with early-onset parkinsonism (EOP). The subjects were 8 patients with early-onset parkinsonism (male/ female = 4/ 4, mean age; 51.3 years). Four out of 8 patients had a history of smoking (smokers). To estimate the effects of nicotine gum, the scores on the Unified Parkinson's Disease Rating Scale (UPDRS) and auditory event-related potentials (ERPs) were studied before and after taking nicotine gum in the EOP patients. In smokers, UPDRS scores improved by more than 10 % and the P300 latency of auditory ERPs was shortened by more than 30 msec. In contrast, nicotine had no remarkable effects on UPDRS scores or auditory ERPs in non-smokers. We suggest that nicotine chewing gum may be a possible choice for the treatment of patients with EOP, especially when they are smokers.