The treatment of Parkinson's disease is reviewed. The rationale for using selegiline (deprenyl) as the first treatment in recently diagnosed patients is presented. Selegiline delays the need for levodopa; however, it is unclear whether this results from a symptomatic or a neuroprotective effect of selegiline. Levodopa combined with a decarboxylase inhibitor is the principal treatment for patients with moderate or marked symptoms. There is little evidence that levodopa has a deleterious effect on the court of Parkinson's disease. The relationship of levodopa to dyskinesias and response fluctuations is discussed. Pharmacokinetic and pharmacodynamic studies suggest that continuous dopaminergic stimulation may be superior to intermittent pulse therapy. The best approximation to continuous stimulation is the use of long-acting levodopa-carbidopa preparations supplemented by dopamine agonists.