This study investigated the effects of OPC in comparison with placebo on levodopa pharmacokinetics, tolerability and safety, COMT activity and motor response to levodopa in Parkinson's disease (PD) patients with motor fluctuations.This was a randomized, multicentre, double-blind and placebo-controlled study in four parallel groups of PD patients treated with standard-release 100/25 mg levodopa/carbidopa or levodopa/benserazide and with motor fluctuations (wearing-OFF phenomenon).