Dopamine D-1 receptors were analyzed in the caudate nucleus, putamen, pallidum, substantia nigra and nucleus accumbens in 20 patients with Parkinson's disease and in 18 age-matched controls by the binding of [3H]flupenthixol. The binding was decreased in the substantia nigra in those parkinsonian patients who were not treated with levodopa. A significantly increased number of D-1 receptors was found in the putamen of patients with Parkinson's disease, especially in those who were treated with levodopa. The increased binding of [3H]flupenthixol was most prominent in those six parkinsonian patients who still had therapeutic response to levodopa. In addition, orofacial dyskinesias were seen in three of these patients. The results of this study indicate that there may be denervation supersensitivity of striatal neurons and also a loss of striatonigral neurons in Parkinson's disease.