BACKGROUND: Most patients with obsessive-compulsive disorder (OCD) show only partial reduction of symptoms with standard therapy. Recent imaging data suggests glutamatergic dysfunction in the corticostriatal pathway in OCD. We investigated the efficacy of augmentation therapy with riluzole, a glutamate-modulating agent, in treatment-resistant OCD. METHODS: Thirteen patients aged between 18 and 65 years with a primary diagnosis of OCD that had proven resistant to standard treatment were treated with the addition of riluzole to their existing pharmacotherapy. Yale-Brown Obsessive Compulsive Scale (Y-BOCS), Hamilton Depression Inventory (HAM-D), and Hamilton Anxiety Inventory (HAM-A) scores were obtained weekly. RESULTS: Thirteen treatment-resistant OCD patients received riluzole 50 mg twice a day. Y-BOCS scores improved significantly over time. Of 13 patients, 7 (54%) demonstrated a >35% reduction in Y-BOCS scores, and 5 (39%) were categorized as treatment responders. HAM-D and HAM-A scores for the group also significantly improved over time. Riluzole was well tolerated with no serious adverse effects noted. CONCLUSIONS: Riluzole appears to have significant antiobsessional, antidepressant, and antianxiety properties. The addition of this agent may be of practical clinical benefit in patients with OCD.