Patients with bipolar disorder who are not benefiting satisfactorily on their current medications are eligible to participate in this study. Candidates will be screened with a psychiatric evaluation, routine blood tests, a urine test and other tests needed to monitor medications. Participants will be randomly assigned to one of two groups: one group will receive 6 grams of omega-3 fatty acid every day for 16 weeks; the second will receive a placebo (inactive capsule). In addition, patients in both groups will continue to take their previous medications. Every 2 weeks, all patients will have their vital signs checked and be evaluated for side effects and mood changes. At the end of the 16-week study period, all patients will be given the opportunity to continue in the study for another 8 months and receive active drug (omega-3 fatty acid). Patients who continue will be evaluated once a month and will have blood drawn on the last visit for routine tests.