Apomorphine (1.5 or 3 mg) or placebo was acutely administered to choreic patients affected by Huntington's disease in a double-blind fashion. The patients were evaluated before the administration, and at 15-min intervals for 2 h afterward, by means of a rating scale for Huntington's disease. As compared to baseline, the total score improved by 38.54% after 1.5 mg and by 30.41% after 3 mg; no variations were observed after placebo. Several items of the scale improved after the administration of 1.5 mg. An average 35.25% improvement was observed in items measuring the intensity of chorea (at rest, with arms outstretched, during conversation, and voluntary movements of the limbs); in addition, motor impersistence (as measured by tongue protrusion) and the capability to suppress associated movements (as measured by head movements during saccades) improved by an average of 31.46 and 61%, respectively. Some items of the scale improved after the administration of 3 mg. Items measuring the intensity of chorea improved by an average 30.41%; in addition, the extent of vertical gaze improved by 63.77%. These data indicate that apomorphine brings about a transient symptomatic improvement of chorea and of other associated clinical features in Huntington's disease. The time course observed for the antichoreic activity is only partially consistent with the antiparkinsonian action of apomorphine.