Lisuride at a mean daily dose of 3 mg was given to 48 patients with idiopathic Parkinson's disease. Twenty received lisuride alone (Group A) and 36 received lisuride + L-Dopa + peripheral decarboxylase inhibitors (Group B). Dropouts were due primarily to lack of efficacy in Group A patients and to mental side effects in Group B patients. The patients who remained in the study for the full 4 years showed distinct improvement, which was maintained. Group A patients did not have the on-off phenomenon or abnormal involuntary movements.