The antidyskinetic potential of the glutamate NMDA receptor channel blocker amantadine was evaluated in four levodopa-primed parkinsonian monkeys using two different regimens (1.25 or 2.5 mg/kg administered subcutaneously twice daily for 3-6 days). When administered with a relatively low dose of levodopa, amantadine produced a near-total suppression of choreiform dyskinesias and a substantial reduction in dystonic dyskinesias at the expense of a significant reduction in antiparkinsonian response. With a high dose of levodopa, amantadine had a smaller but still significant effect on dyskinesias without altering the antiparkinsonian response. These results lend support to the view that glutamate receptor-mediated mechanisms contribute to levodopa-induced dyskinesias. They also suggest that amantadine could alleviate such complications in parkinsonian patients, especially with careful dose optimization.