Gabapentin is a new adjunctive medication to antiseizure therapies. Anecdotal evidence suggests that it may also help to alleviate mood symptoms in patients with bipolar illness. An open-label study examined the effects of adjunctive gabapentin in bipolar patients with mixed symptoms who had previously demonstrated only partial treatment responses. Mood ratings and side-effect profiles were followed weekly in 10 patients for 1 month. Decreases in Hamilton depression (P < 0.05) and Bech mania ratings (P < 0.01) were evident in the first week of treatment and were sustained. Potent early improvements were noted in early, middle, and late insomnia. The results suggest that gabapentin may be of benefit to bipolar patients who only partially respond to other mood stabilizers. A favorable side-effect profile and rapid action make this drug an attractive choice as an adjunctive therapy.