The purpose of this study is to determine whether oral intake of COMT inhibitors affects the smooth plasma levodopa levels achieved by intestinal levodopa/carbidopa infusion in advanced Parkinson's disease patients. The hypothesis is that COMT inhibitors make plasma concentrations of levodopa more fluctuating.

The aim is to measure variability in plasma levodopa levels during the following three treatments:

Day 1: Duodopa in individually optimised dose Day 2: 80% of optimised Duodopa dose + two tablets of entacapone at t=0 hours and at t= 6 hours Day 3: 80% of optimised Duodopa dose + two tablets of tolcapone at t=0 hours and at t= 6 hours Plasma samples for determination of levodopa concentrations will be taken every 30 minutes during 8 hours. Video recordings will be performed every 30 min during 8 hours, for later blinded assessments by 2-3 experts. Sequences will be in randomised order. Patient self-scores regarding mobility will be recorded, every 30 min during 8 hours.

Inclusion Criteria:

• Parkinson's disease
• Duodopa treatment ongoing
• Hoehn & Yahr stage 3-5 at worst

Exclusion Criteria:

• Ongoing treatment with COMT inhibitors
• Dementia
• Psychosis
• Treatment with typical neuroleptics
• Contraindications for entacapone or tolcapone