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The question of the relationship between contingent negative variation and the mechanisms controlling motor and mental functions has received inadequate study. The aims of the present work were to investigate the relationship between the early and late phases of contingent negative variation and the state of motor and mental functions in patients with Parkinson's disease and to study the effects of levodopa on contingent negative variation. Patients with Parkinson's disease showed significant decreases in the amplitudes and areas of both phases of contingent negative variation as compared with subjects of similar age. Correlation analysis demonstrated a negative relationship between the extent of impairment of coordinatory muscle interactions and the amplitudes of both phases of this variation (p < 0.01). There was a positive relationship between the magnitudes of both phases and the state of mental functions, particularly memory (p < 0.05). Treatment of patients with Parkinson's disease with levodopa was followed by a significant increase in the late phase (p < 0.05). The results obtained here provide evidence for the important role of structures supporting both direct motor control and mental functions in forming both phases of contingent negative variation. The greater effect of levodopa on the late phase of contingent negative variation suggests that the efferent system of the basal ganglia has a greater role in generating the late phase than in organizing the early phase of the variation.