The efficacy of pergolide as adjunct to levodopa therapy was compared to that of bromocriptine in 12 parkinsonian patients with fluctuating motor disability and levodopa-induced dyskinesias (mean age of onset, 50.6 +/- 8 years; Hoehn and Yahr stage between II and IV; mean basal UPDRS motor score, 30.6 +/- 8.6), in a double-blind crossover study. After an 8-day habituation to each agonist, an acute challenge of a supraliminal dose of levodopa ("levodopa test") was performed in association with either 1 mg pergolide or 10 mg bromocriptine. The delay to onset and the duration of therapeutic benefit, the percentage improvement in motor disability, and the severity of onset and peak-dose dyskinesias were evaluated. Both agonists significantly increased the duration of therapeutic benefit, but pergolide more so than bromocriptine (p = 0.02). Pergolide also tended to reduce the severity of dyskinesias and was globally perceived by the patients to be more efficacious than bromocriptine on parkinsonian symptoms and fluctuations. This study illustrated the usefulness of the "levodopa test" in evaluating, objectively, the effects of dopamine agonists.