We compared the efficacy, safety, an tolerability of pramipexole, an aminobenzathiazol-derived dopamine agonist with novel properties, with those of placebo in advanced PD patients with motor fluctuations under levodopa treatment. Pramipexole improved motor function of patients during "on" and "off" periods, decreased the time spent in "off" periods, reduced the severity of "off" periods, decreased disability and PD severity during "on" and "off" periods, as assessed by the Unified Parkinson Disease Rating Scale, and permitted a reduction in levodopa dosage. Adverse effects related to the central nervous system were similar to those reported with other dopamine agonists, and the gastrointestinal and cardiovascular tolerability of the compound was satisfactory.