Background: Glutamatergic system abnormalities are implicated in the pathophysiology and treatment of both major depressive disorder and bipolar depression (BDep). Subsequent to studies demonstrating the rapid and robust antidepressant effects of ketamine, an N-methyl-D-aspartate receptor antagonist, other glutamatergic modulators are now being studied in clinical trials of mood disorders. A previous open-label study found that riluzole, administered in combination with the mood stabilizer lithium, had antidepressant effects. Methods: We conducted a randomized, double-blind, placebo-controlled trial of riluzole monotherapy for the treatment of BDep. Nineteen subjects aged 18 to 70 years with bipolar disorder currently experiencing a depressive episode were tapered off of excluded medications and randomized to receive riluzole (50-200 mg/d) or placebo for 8 weeks. Rating scale scores (Montgomery-angstrom sberg Depression Rating Scale, Hamilton Rating Scale for Depression, Hamilton Rating Scale for Anxiety, and Young Mania Rating Scale) were obtained weekly. Results: No significant differences in depressive symptoms were observed between subjects treated with riluzole and those receiving placebo (P = 0.12). Anxiety scores were significantly lower in the placebo group (P = 0.046). An interim analysis was conducted that resulted in stopping the study because of futility; no subjects had achieved treatment response. Conclusions: Although we found no change in severity of depressive symptoms in BDep patients receiving riluzole compared with placebo, this trial was limited by the relatively high number of subject withdrawals and the small sample size. Thus, while riluzole monotherapy did not demonstrate efficacy for BDep, further studies examining riluzole as adjunctive therapy for this disorder may be warranted.