The progress of 50 previously untreated patients with idiopathic Parkinson's disease taking maximum tolerated doses of bromocriptine is described. Twenty-eight showed sustained benefit, defined as a 25% improvement in disability scores for at least 1 year, and in five this improvement persisted for longer than 5 years. However, there was a tendency for deterioration to occur after about 2 years of bromocriptine. Fewer of the late complications associated with levodopa therapy were seen in those taking bromocriptine, and drug-induced dyskinesia was seen in only one patient. Fourteen early bromocriptine failures subsequently responded well to levodopa, but the addition of levodopa to patients showing late deterioration on long-term bromocriptine was unsuccessful. These results indicate that the total duration of effective drug treatment for Parkinson's disease cannot be extended by giving bromocriptine before commencing levodopa.