Pergolide is a potent, direct-acting dopamine agonist used in treating Parkinson's disease. It is an agonist found recently to have high affinity for D3 receptors. The affinity of pergolide for D1 receptors is lower than for D2 receptors, and there have been some reports that it may not interact with D1 receptors in vivo at doses used to activate D2 receptors. A growing body of evidence suggests that pergolide does occupy and activate D1 receptors in vivo, although the relevance to therapeutic efficacy in Parkinson's disease needs further study.