The increasingly recognized occurrence of dementia in Parkinson's disease (PD) has prompted study of cognitive evoked potentials in this disorder. The P300 wave is related to cognitive performance, while the contingent negative variation (CNV) may reflect dopaminergic function. We measured P300 and CNV in 21 nondemented PD patients and compared them to elderly controls. The P300 was recorded from Cz with linked ear reference. 3,000 and 1,000 Hz tones were presented in an 80:20 ratio at 76 dBSL interstimulus interval was 1.1 seconds, and filter bandpass was 1-100 Hz. CNV recording utilized a 2000 Hz tone followed after 1.5 seconds by a light flash and button press, and was recorded from Fz with linked ear reference, 10-second analysis time, and 0.1-20 Hz filter bond pass. N200 and P300 amplitudes were significantly longer and latency significantly lower in PD patients than in controls, and P300 latency was correlated with composite score on cognitive tests. CNV amplitude was significantly reduced in PD patients, but was correlated with measures of motor disability rather than cognition. These findings suggest that bradyphrenia may occur in nondemented PD patients, and that P300 may measure cognitive changes in PD. CNV may be a dopaminergic slow potential and may correlate with motor function in nondemented PD patients.