Ten patients who had Parkinson's disease with disabling dyskinesia were included in this study to evaluate the role of mental (mental calculation) and motor (flexion/extension of right fingers, flexion/extension of left fingers, flexion/extension of the neck, speaking aloud) tasks on the worsening of peak-dose dyskinesia following administration of an effective single dose of apomorphine. Compared with the score at rest (1.3+/-0.3), a significant aggravation of the dyskinesia score was observed during speaking aloud (5.2+/-1.1, p<0.05), movements of right (4.5+/-1.0, p<0.05) and left (3.7+/-0.8, p<0.05) fingers, movements of the neck (5.1+/-1.0, p<0.05), and mental calculation (3.1+/-1.0, p<0.05). These results suggest that activation tasks such as "speaking aloud" could be used for objective assessment of dyskinesia severity.