The Authors introduce some questions concerning cognitive impairment in Parkinsonian patients and they focus the attention on 'bradyphrenia'. They briefly discuss the methodological difficulties in studying this kind of disturbances in Parkinson's disease (PD) and the approach to this problem with the help of the Event-Related Potentials or ERPs. Finally, they review literature and their data on Contingent Negative Variation (CNV) and P300 in PD and conclude that interesting and useful informations can be obtained by means of the electrophysiological methods.