Medical management of Parkinson's disease consists of two strategies. A presynaptic strategy attempts to maintain physiologic synaptic concentrations of dopamine, usually by individualizing delivery of levodopa (or exogenous dopamine) by varying the rate of gastrointestinal absorption or blood-brain barrier passage. A postsynaptic strategy bypasses degenerating nigrostriatal neurons by stimulating striatal neurons directly with dopamine agonists. With advancing disease, motor fluctuations appear, related to physiologic changes that narrow the window of levodopa concentration in which symptoms are under control. Then it becomes necessary to add dopamine agonists to therapy.