We evaluated the severity of motor disability and dyskinesias in seven levodopa-responsive patients with Parkinson's disease after an acute challenge with the mixed dopamine agonist, apomorphine, before and after the administration of fluoxetine (20 mg twice per day) for 11 +/- 1 days. After fluoxetine treatment, there was a significant 47% improvement (p < 0.05) of apomorphine-induced dyskinesias without modification of parkinsonian motor disability. The dyskinesias were reduced predominantly in the lower limbs during the onset and disappearance of dystonic dyskinesias (onset- and end-of-dose dyskinesias) and in the upper limbs during choreic mid-dose dyskinesias. The results suggest that increased brain serotoninergic transmission with fluoxetine may reduce levodopa- or dopamine agonist-induced dyskinesias without aggravating parkinsonian motor disability.