We investigated whether administration of the catechol-O-methyl transferase (COMT) inhibitor entacapone, at doses of 200 mg and 400 mg, alters the pharmacokinetics of apomorphine in Parkinson's disease patients experiencing severe motor fluctuations. In addition, the pharmacodynamics and safety of entacapone and apomorphine coadministration in these patients were examined. The study followed a three-sequence, three-period, crossover design. Patients were randomly assigned to one of three sequences that included single oral doses of entacapone 200 mg, entacapone 400 mg, and placebo in a predefined order. On 3 separate test days, study treatment was administered before apomorphine. The study evaluations (pharmacokinetics, tapping test, and dyskinesia evaluation [Abnormal Involuntary Movements Scale - AIMS]) were performed on these days. Furthermore, Unified Parkinson Disease Rating Scale (UPDRS) scores were evaluated at baseline and study end. Pharmacokinetic parameters for apomorphine (C(max), AUC, t(max), t(1/2)) were unchanged by the administration of entacapone, and changes in both the tapping test and AIMS score were similar with all treatments (entacapone 200 mg, entacapone 400 mg, and placebo). There was no significant difference in mean total UPDRS scores between baseline and study end. The administration of entacapone did not change the pharmacokinetic or pharmacodynamic effects of apomorphine in these patients or prolong the clinical effect of apomorphine. Thus, apomorphine may be safely administered to patients receiving therapy with levodopa and entacapone, providing a useful addition to treatment for patients with advanced Parkinson's disease.