The objective of this study was to evaluate the effect of riluzole on dyskinesia and the duration of the ON state in patients with Parkinson disease (PD). The authors studied 16 PD patients with levodopa-induced dyskinesia. All patients initially received an apomorphine dose intended to induce the motor function benefit (ON state) generally accompanied by dyskinesia. They evaluated the patients during the OFF and ON states using the UPDRS-III, UPDRS-IV, and Larsen scales, and measured the duration of the ON state. Patients were randomly assigned to receive either riluzole (50 mg bid) or placebo for 7 consecutive days (8 patients in each group). The authors did not interrupt previously prescribed medication. Following the 7-day period, they carried out similar evaluation procedures before and after another apomorphine challenge. Mean UPDRS-IV scores were 6.1 points and 6.0 points before and after riluzole therapy respectively. For the placebo group, the scores were 6.9 points and 6.6 points for the initial and final evaluations respectively. Larsen scale had mean scores of 9.2 points and 9.9 points for the pre- and postriluzole periods, and 10.2 points and 9.6 points for pre- and post-placebo evaluations respectively. The ON state was 33.5% lengthier after 7 days of riluzole and 28.0% lengthier after placebo. They could not find any statistical differences between the 2 groups. Short-term riluzole administration in PD patients was not able to reduce apomorphine-induced dyskinesia but could extend the ON state duration, although this did not reach statistical significance.