We used pergolide to treat 10 patients with idiopathic Parkinson's disease who had first responded to, and then failed, bromocriptine therapy. At the end of 5 years, patients had improved when compared with study entry. Peak efficacy, equal with both drugs, was seen at 12 months. After a mean treatment of 29 months, bromocriptine was no longer effective, but pergolide was still beneficial.