Recent anecdotal single case reports have suggested that the new antiepileptic drug gabapentin might be effective in the treatment of manic episodes and in the prophylaxis of bipolar disorder. In the present open trial, 14 patients with acute mania were treated for up to 21 days with gabapentin in a dose range from 1200 to 4800 mg/day. Six patients were treated with gabapentin as add-on medication and 8 patients were treated with a high dose of gabapentin alone. Gabapentin was both efficacious and safe when applied in combination with other drugs such as lithium and valproic acid. All patients in the add-on group and 4/8 patients on gabapentin monotherapy finished the 21 day protocol. Analysis of the scores of the Bech-Rafaelsen Mania Assessment Scale (BRMAS) of these patients showed that the mean BRMAS score declined from 37.7 to 7.8 on day 21 in the add-on group and from 27.8 to 9.0 in 4/8 patients finishing 21 days in the monotherapy group. It is suggested that gabapentin monotherapy might be useful in selected patients to treat modest but not severe manic states. In addition, gabapentin in conjunction with other effective mood stabilisers seems to be safe and efficacious in the treatment of severe mania.