15 years' experience with Parkinson's disease treated with levodopa was compared to the 15 years before the advent of levodopa. Progression to severe disability and death was prolonged, at each stage of severity, by 3 to 5 years. At each duration of illness, the percentage of patients with severe disability was reduced significantly. There was some indication that independence was prolonged by early treatment. Life expectancy was increased to approximately that of the unaffected population. However, especially with patients with onset of disease before the age of 50, fluctuations of therapeutic response and severe abnormal involuntary movements interfered with satisfactory therapeutic results. Supplemental bromocriptine produced a smoother therapeutic response and decreased "off" period dystonia and leg pains in over 70% of patients. At dosages below 20 mg daily, it was not particularly effective in severely affected disabled patients. Adverse reactions prevented the use of bromocriptine in less than 20% of patients.