This is a randomised, double-blind, placebo-controlled, dose-ranging multicentre study with parallel groups. Patients will be equally randomized to receive 0.5 mg, 1 mg or 2 mg of E2007 or matching placebo for 12 weeks (84 days) in addition to their stable antiparkinsonian treatment. The study will involve two overnight in-patient stays. The first of these will be for 2 nights and 3 days and the second will be for 1 night and 2 days. The remainder of the study will be conducted on an outpatient basis.