The severity of parkinsonian motor disability and dyskinesias was evaluated in seven levodopa-responsive patients with Parkinson's disease after an acute challenge with the mixed dopamine agonist apomorphine, before and after low-dose clozapine (50 mg) for 18 +/- 2 days. There was a significant 59% improvement (p < 0.05) of apomorphine-induced dyskinesias without aggravation of parkinsonian motor disability following clozapine treatment. The results suggest that low-dose clozapine, already shown to improve psychotic symptoms, may help to reduce severe levodopa-induced dyskinesias in parkinsonian patients.