A double-blind crossover study was performed in 12 patients with idiopathic parkinsonism to compare their response to bromocriptine with their response to previous optimal drug treatment, including levodopa. There was a 26 percent overall improvement with bromocriptine; rigidity, tremor, and facial expression showed the greatest response. Seven of eight patients who were taking levodopa at the beginning of the study were taken off the drug completely. Adverse reactions were transient and dose-dependent. Bromocriptine promises to be an effective new therapeutic agent in the treatment of idiopathic parkinsonism.