Oxiperomide, a new dopamine-receptor antagonist, was found to decrease dyskinesias in patients with Parkinson's disease receiving levodopa or other dopamine agonists without necessarily increasing Parkinsonian symptoms. Oxiperomide also decreased spontaneous dyskinesias in those with tics and chorea and to a less extent in those with torsion dystonia, without necessarily causing Parkinsonism. These results provide evidence that more than one population of dopamine receptors exist in the extra pyramidal system, and encourage the search for selective dopamine antagonists.