▴ Entacapone is a potent, orally active, selective inhibitor of peripheral catechol-O-methyltransferase (COMT), which has therapeutic potential as an adjunct to levodopa therapy in patients with Parkinson's disease.▴ Entacapone decreases peripheral conversion of levodopa to 3-O-methyldopa and improves central uptake of levodopa.▴ Addition of entacapone to levodopa/carbidopa or levodopa/benserazide increased the duration of clinical response in patients with Parkinson's disease: the duration of ‘on’ time was increased and the duration of ‘off’ time was decreased.▴ Levodopa requirements were reduced in patients with Parkinson's disease who received adjunctive entacapone therapy.▴ Entacapone was generally well tolerated, with few reported adverse events.