Patients, ages 18 or older, with a diagnosis of Bipolar I or II disorder, depressed (without psychotic features), will be randomized to double-blind treatment to receive either felbamate (600-3000 mg/day) or placebo for a period of 8 weeks. Following this acute period, the patients will receive treatment as clinically indicated. Approximately 52 patients with treatment-resistant acute bipolar depression will be enrolled in the study.