A duodenal levodopa (L-dopa) and carbidopa infusion has been developed to stabilize plasma levels of L-dopa, in order to reduce existing motor response fluctuations. Stable plasma levels have been shown to reduce these fluctuations significantly. A constant duodenal infusion with an L-dopa solution can improve response fluctuations, however L-dopa has very poor solubility. Only in an acidic environment can L-dopa be dissolved in large volumes. To supply 1 day of infusion with the conventional L-dopa solution, ∼4–5 liters are necessary, an inconvenience to most patients. With L-dopa/carbidopa infusion, L-dopa and carbidopa are concentrated in a water-based gel-like suspension to 20 mg/mL, which has reduced the infusion volumes to <100 mL/day.