The semisynthetic ergoline dopamine agonist pergolide has demonstrated activity at pre- and postsynaptic dopamine D-2 receptors in in vitro and in vivo animal studies. However, unlike other dopamine agonists such as bromocriptine, pergolide also has agonist activity at dopamine D-1 receptors. Certain other pharmacological effects of pergolide, such as reduction of dopamine turnover and effects on free radical scavenging enzymes, may be relevant in the early treatment of Parkinson's disease but this has not been conclusively determined. Short and long term noncomparative studies show that pergolide is an effective adjunct to levodopa therapy in patients with advancing Parkinson's disease, reducing the adverse effects of long term levodopa monotherapy and often enabling a reduction in levodopa dosage. In placebo comparisons pergolide was generally more effective than placebo and was associated with benefits similar to those seen in noncomparative studies. Longitudinal comparisons in individual patients indicate that the antiparkinsonian efficacy of pergolide is similar to that of mesulergine, lergotrile and lisuride, and may be superior to that of bromocriptine. Controlled comparisons with bromocriptine tend to support this latter finding. Studies evaluating the efficacy of pergolide as monotherapy early in the course of Parkinson's disease have shown the drug to be effective, but opinion is divided as to the value of early treatment with dopamine agonists (as opposed to levodopa monotherapy). Thus, pergolide is an effective adjunct to levodopa therapy in patients with advanced Parkinson's disease and may have a role in the treatment of early disease if its postulated beneficial effects on disease progression are proven.