Dyskinesias occur in the majority of patients with Parkinson's disease chronically treated with L-DOPA and also occur in several nonhuman primate species after 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP) and L-DOPA treatment. The common marmoset (Callithrix jacchus) shows parkinsonian motor deficits after MPTP administration, and we now report dyskinesias occurring in this species during chronic L-DOPA exposure. Marmosets rendered chronically parkinsonian after MPTP administration were treated orally with L-DOPA plus carbidopa for 3 weeks. After several days the animals began to display chorea, choreoathetosis, and dystonia. The severity of dyskinesias varied between the animals, with the most severely parkinsonian animals displaying the most dyskinetic movements. Each animal showed an idiosyncratic pattern of dyskinesias, which was highly reproducible. These L-DOPA-primed animals also received other D2 D1, and mixed D1/D2 agonist drugs. Quinpirole, bromocriptine, pergolide, apomorphine, and A-77636 all produce dyskinesias that were identical in character to those seen after L-DOPA administration, but the D1 agonist A-77636 gradually abolished dyskinesias while preserving its antiparkinsonian activity. The MPTP-treated marmoset provides a useful model in which to study dyskinesias in Parkinson's disease and to examine new therapeutic strategies aimed at alleviating this common side effect of chronic dopamine replacement therapy.