We evaluated the efficacy, safety and tolerability of a new dopamine D-2 receptor agonist, pramipexole [(S)-2-amino-4,5,6,7-tetrahydro-6-propylamino-benzathiazol-dihydro chloride], as adjunctive therapy in patients with advanced Parkinson's disease (PD). Twenty-four PD patients with motor fluctuations were treated in an 11 week prospective, single-blind parallel-group, placebo-controlled trial. The pramipexole treated group experienced a significant improvement in "off" time functioning as measured by the activities of daily living portion of the United Parkinson's Disease Rating Scale. In addition, the active treatment group was able to reduce total levodopa dose by 30% (p < 0.05). Pramipexole was well tolerated and the side effects reported were typical of other dopamine agonists. We conclude that pramipexole has antiparkinsonian effects which make it potentially useful in the treatment of motor fluctuations in PD.