Nine patients with idiopathic Parkinson9s disease were treated with pergolide to a daily maintenance dose of 2.2 ± 0.9 mg (mean ± SD) for 17.3 ± 8.3 months. After 1 month, there was an average 68% increase in mobile on-time, but the improvement declined to 30% by 6 months, 23% by 1 year, and virtually disappeared by 18 months of therapy. Pergolide was discontinued in seven patients because of loss of efficacy (4 patients), confusion (1 patient), or myocardial infarction or ventricular ectopy (2 patients). Partial but temporary restoration of mobility was observed in seven patients who were switched to an alternate-day dosing schedule after 9.2 ± 2.4 months. Two patients with advanced Shy-Drager syndrome were treated with pergolide without benefit.